[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering #123867

MattPD · 2025-01-22T01:50:17Z

A proposed fix for #95611 [OpenMP][SIMD] ordered has no effect in a loop SIMD region as of LLVM 18.1.0

Changes:

Implement new lowering behavior: Conservatively serialize "omp simd" loops that have omp simd ordered directive to prevent incorrect vectorization (which results in incorrect execution behavior of the miscompiled program).

Implementation outline:

We start with the optimistic default initial value of LoopStack.setParallel(/Enable=/true); in CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D).
We only disable the loop parallel memory access assumption with if (HasOrderedDirective) LoopStack.setParallel(/Enable=/false); using the HasOrderedDirective (which tests for the presence of an OMPOrderedDirective).
This results in no longer incorrectly vectorizing the loop when the omp simd ordered directive is present.

Motivation: We'd like to prevent incorrect vectorization of the loops marked with the #pragma omp ordered simd directive which has previously resulted in miscompiled code.

At the same time, we'd like the usage outside of the #pragma omp ordered simd context to remain unaffected: Note that in the test "clang/test/OpenMP/ordered_codegen.cpp" we only "lose" the !llvm.access.group metadata in foo_simd alone.

This is conservative, in that it's possible some of the loops would be possible to vectorize, but we prefer to avoid miscompilation of the loops that are currently illegal to vectorize.

A concrete example follows:

// "test.c"
#include <float.h>
#include <math.h>
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int compare_float(float x1, float x2, float scalar) {
    const float diff = fabsf(x1 - x2);
    x1 = fabsf(x1);
    x2 = fabsf(x2);
    const float l = (x2 > x1) ? x2 : x1;
    if (diff <= l * scalar * FLT_EPSILON)
        return 1;
    else
        return 0;
}

#define ARRAY_SIZE 256

__attribute__((noinline)) void initialization_loop(
    float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) {
    const float max = 1000.0;
    srand(time(NULL));
    for (int r = 0; r < ARRAY_SIZE; r++) {
        for (int c = 0; c < ARRAY_SIZE; c++) {
            X[r][c] = ((float)rand() / (float)(RAND_MAX)) * max;
            Y[r][c] = X[r][c];
        }
    }
}

__attribute__((noinline)) void omp_simd_loop(float X[ARRAY_SIZE][ARRAY_SIZE]) {
    for (int r = 1; r < ARRAY_SIZE; ++r) {
        for (int c = 1; c < ARRAY_SIZE; ++c) {
#pragma omp simd
            for (int k = 2; k < ARRAY_SIZE; ++k) {
#pragma omp ordered simd
                X[r][k] = X[r][k - 2] + sinf((float)(r / c));
            }
        }
    }
}

__attribute__((noinline)) int comparison_loop(float X[ARRAY_SIZE][ARRAY_SIZE],
                                              float Y[ARRAY_SIZE][ARRAY_SIZE]) {
    int totalErrors_simd = 0;
    const float scalar = 1.0;
    for (int r = 1; r < ARRAY_SIZE; ++r) {
        for (int c = 1; c < ARRAY_SIZE; ++c) {
            for (int k = 2; k < ARRAY_SIZE; ++k) {
                Y[r][k] = Y[r][k - 2] + sinf((float)(r / c));
            }
        }
        // check row for simd update
        for (int k = 0; k < ARRAY_SIZE; ++k) {
            if (!compare_float(X[r][k], Y[r][k], scalar)) {
                ++totalErrors_simd;
            }
        }
    }
    return totalErrors_simd;
}

int main(void) {
    float X[ARRAY_SIZE][ARRAY_SIZE];
    float Y[ARRAY_SIZE][ARRAY_SIZE];

    initialization_loop(X, Y);
    omp_simd_loop(X);
    const int totalErrors_simd = comparison_loop(X, Y);

    if (totalErrors_simd) {
        fprintf(stdout, "totalErrors_simd: %d \n", totalErrors_simd);
        fprintf(stdout, "%s : %d - FAIL: error in ordered simd computation.\n",
                __FILE__, __LINE__);
    } else {
        fprintf(stdout, "Success!\n");
    }

    return totalErrors_simd;
}

Before:

$ clang -fopenmp-simd -O3 -ffast-math -lm test.c -o test && ./test
totalErrors_simd: 15408
test.c : 76 - FAIL: error in ordered simd computation.

clang 19.1.0: https://godbolt.org/z/6EvhxqEhe

After:

$ clang -fopenmp-simd -O3 -ffast-math test.c -o test && ./test
Success!

llvmbot · 2025-01-22T01:52:44Z

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Matt (MattPD)

Changes

A proposed fix for #95611 [OpenMP][SIMD] ordered has no effect in a loop SIMD region as of LLVM 18.1.0

Changes:

Implement new lowering behavior: Conservatively serialize "omp simd" loops that have omp simd ordered directive to prevent incorrect vectorization (which results in incorrect execution behavior of the miscompiled program).

Implementation outline:

We start with the optimistic default initial value of LoopStack.setParallel(/Enable=/true); in CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D).
We only disable the loop parallel memory access assumption with if (HasOrderedDirective) LoopStack.setParallel(/Enable=/false); using the HasOrderedDirective (which tests for the presence of an OMPOrderedDirective).
This results in no longer incorrectly vectorizing the loop when the omp simd ordered directive is present.

Motivation: We'd like to prevent incorrect vectorization of the loops marked with the #pragma omp ordered simd directive which has previously resulted in miscompiled code.

At the same time, we'd like the usage outside of the #pragma omp ordered simd context to remain unaffected: Note that in the test "clang/test/OpenMP/ordered_codegen.cpp" we only "lose" the !llvm.access.group metadata in foo_simd alone.

This is a conservative, in that it's possible some of the loops would be possible to vectorize, but we prefer to avoid miscompilation of the loops that are currently illegal to vectorize.

A concrete example follows:

// "test.c"
#include &lt;float.h&gt;
#include &lt;math.h&gt;
#include &lt;omp.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;time.h&gt;

int compare_float(float x1, float x2, float scalar) {
    const float diff = fabsf(x1 - x2);
    x1 = fabsf(x1);
    x2 = fabsf(x2);
    const float l = (x2 &gt; x1) ? x2 : x1;
    if (diff &lt;= l * scalar * FLT_EPSILON)
        return 1;
    else
        return 0;
}

#define ARRAY_SIZE 256

__attribute__((noinline)) void initialization_loop(
    float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) {
    const float max = 1000.0;
    srand(time(NULL));
    for (int r = 0; r &lt; ARRAY_SIZE; r++) {
        for (int c = 0; c &lt; ARRAY_SIZE; c++) {
            X[r][c] = ((float)rand() / (float)(RAND_MAX)) * max;
            Y[r][c] = X[r][c];
        }
    }
}

__attribute__((noinline)) void omp_simd_loop(float X[ARRAY_SIZE][ARRAY_SIZE]) {
    for (int r = 1; r &lt; ARRAY_SIZE; ++r) {
        for (int c = 1; c &lt; ARRAY_SIZE; ++c) {
#pragma omp simd
            for (int k = 2; k &lt; ARRAY_SIZE; ++k) {
#pragma omp ordered simd
                X[r][k] = X[r][k - 2] + sinf((float)(r / c));
            }
        }
    }
}

__attribute__((noinline)) int comparison_loop(float X[ARRAY_SIZE][ARRAY_SIZE],
                                              float Y[ARRAY_SIZE][ARRAY_SIZE]) {
    int totalErrors_simd = 0;
    const float scalar = 1.0;
    for (int r = 1; r &lt; ARRAY_SIZE; ++r) {
        for (int c = 1; c &lt; ARRAY_SIZE; ++c) {
            for (int k = 2; k &lt; ARRAY_SIZE; ++k) {
                Y[r][k] = Y[r][k - 2] + sinf((float)(r / c));
            }
        }
        // check row for simd update
        for (int k = 0; k &lt; ARRAY_SIZE; ++k) {
            if (!compare_float(X[r][k], Y[r][k], scalar)) {
                ++totalErrors_simd;
            }
        }
    }
    return totalErrors_simd;
}

int main(void) {
    float X[ARRAY_SIZE][ARRAY_SIZE];
    float Y[ARRAY_SIZE][ARRAY_SIZE];

    initialization_loop(X, Y);
    omp_simd_loop(X);
    const int totalErrors_simd = comparison_loop(X, Y);

    if (totalErrors_simd) {
        fprintf(stdout, "totalErrors_simd: %d \n", totalErrors_simd);
        fprintf(stdout, "%s : %d - FAIL: error in ordered simd computation.\n",
                __FILE__, __LINE__);
    } else {
        fprintf(stdout, "Success!\n");
    }

    return totalErrors_simd;
}

Before:

$ clang -fopenmp-simd -O3 -ffast-math -lm test.c -o test &amp;&amp; ./test
totalErrors_simd: 15408
test.c : 76 - FAIL: error in ordered simd computation.

clang 19.1.0: https://godbolt.org/z/6EvhxqEhe

After:

$ clang -fopenmp-simd -O3 -ffast-math test.c -o test &amp;&amp; ./test
Success!

Patch is 42.63 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/123867.diff

3 Files Affected:

(modified) clang/lib/CodeGen/CGStmtOpenMP.cpp (+72)
(modified) clang/test/OpenMP/ordered_codegen.cpp (+116-116)
(added) clang/test/OpenMP/simd_conservative_ordered.c (+111)

diff --git a/clang/lib/CodeGen/CGStmtOpenMP.cpp b/clang/lib/CodeGen/CGStmtOpenMP.cpp
index 8e694b95dc7e73..db2531b69ca272 100644
--- a/clang/lib/CodeGen/CGStmtOpenMP.cpp
+++ b/clang/lib/CodeGen/CGStmtOpenMP.cpp
@@ -2457,10 +2457,82 @@ static void emitSimdlenSafelenClause(CodeGenFunction &CGF,
   }
 }
 
+// Check for the presence of an `OMPOrderedDirective`,
+// i.e., `ordered` in `#pragma omp ordered simd`.
+//
+// Consider the following source code:
+// ```
+// __attribute__((noinline)) void omp_simd_loop(float X[ARRAY_SIZE][ARRAY_SIZE]) {
+//     for (int r = 1; r < ARRAY_SIZE; ++r) {
+//         for (int c = 1; c < ARRAY_SIZE; ++c) {
+// #pragma omp simd
+//             for (int k = 2; k < ARRAY_SIZE; ++k) {
+// #pragma omp ordered simd
+//                 X[r][k] = X[r][k - 2] + sinf((float)(r / c));
+//             }
+//         }
+//     }
+// }
+// ```
+//
+// Suppose we are in `CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D)`.
+// By examining `D.dump()` we have the following AST containing `OMPOrderedDirective`:
+//
+// ```
+// OMPSimdDirective 0x1c32950
+// `-CapturedStmt 0x1c32028
+//   |-CapturedDecl 0x1c310e8
+//   | |-ForStmt 0x1c31e30
+//   | | |-DeclStmt 0x1c31298
+//   | | | `-VarDecl 0x1c31208  used k 'int' cinit
+//   | | |   `-IntegerLiteral 0x1c31278 'int' 2
+//   | | |-<<<NULL>>>
+//   | | |-BinaryOperator 0x1c31308 'int' '<'
+//   | | | |-ImplicitCastExpr 0x1c312f0 'int' <LValueToRValue>
+//   | | | | `-DeclRefExpr 0x1c312b0 'int' lvalue Var 0x1c31208 'k' 'int'
+//   | | | `-IntegerLiteral 0x1c312d0 'int' 256
+//   | | |-UnaryOperator 0x1c31348 'int' prefix '++'
+//   | | | `-DeclRefExpr 0x1c31328 'int' lvalue Var 0x1c31208 'k' 'int'
+//   | | `-CompoundStmt 0x1c31e18
+//   | |   `-OMPOrderedDirective 0x1c31dd8
+//   | |     |-OMPSimdClause 0x1c31380
+//   | |     `-CapturedStmt 0x1c31cd0
+// ```
+//
+// Note the presence of `OMPOrderedDirective` above:
+// It's (transitively) nested in a `CapturedStmt` representing the pragma annotated compound statement.
+// Thus, we need to consider this nesting and include checking the `getCapturedStmt` in this case.
+static bool hasOrderedDirective(const Stmt *S) {
+  if (isa<OMPOrderedDirective>(S))
+    return true;
+
+  if (const auto *CS = dyn_cast<CapturedStmt>(S))
+    return hasOrderedDirective(CS->getCapturedStmt());
+
+  for (const Stmt *Child : S->children()) {
+    if (Child && hasOrderedDirective(Child))
+      return true;
+  }
+
+  return false;
+}
+
+static void applyConservativeSimdOrderedDirective(const Stmt &AssociatedStmt, LoopInfoStack &LoopStack) {
+  // Check for the presence of an `OMPOrderedDirective`
+  // i.e., `ordered` in `#pragma omp ordered simd`
+  bool HasOrderedDirective = hasOrderedDirective(&AssociatedStmt);
+  // If present then conservatively disable loop vectorization
+  // analogously to how `emitSimdlenSafelenClause` does.
+  if (HasOrderedDirective)
+    LoopStack.setParallel(/*Enable=*/false);
+}
+
 void CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D) {
   // Walk clauses and process safelen/lastprivate.
   LoopStack.setParallel(/*Enable=*/true);
   LoopStack.setVectorizeEnable();
+  const Stmt *AssociatedStmt = D.getAssociatedStmt();
+  applyConservativeSimdOrderedDirective(*AssociatedStmt, LoopStack);
   emitSimdlenSafelenClause(*this, D);
   if (const auto *C = D.getSingleClause<OMPOrderClause>())
     if (C->getKind() == OMPC_ORDER_concurrent)
diff --git a/clang/test/OpenMP/ordered_codegen.cpp b/clang/test/OpenMP/ordered_codegen.cpp
index 67285cfaef34d5..5cd95f1927e5ce 100644
--- a/clang/test/OpenMP/ordered_codegen.cpp
+++ b/clang/test/OpenMP/ordered_codegen.cpp
@@ -572,30 +572,30 @@ void foo_simd(int low, int up) {
 // CHECK1-NEXT:    store i32 0, ptr [[DOTOMP_IV]], align 4
 // CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND:%.*]]
 // CHECK1:       omp.inner.for.cond:
-// CHECK1-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3:![0-9]+]]
-// CHECK1-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
+// CHECK1-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4
 // CHECK1-NEXT:    [[ADD6:%.*]] = add i32 [[TMP9]], 1
 // CHECK1-NEXT:    [[CMP7:%.*]] = icmp ult i32 [[TMP8]], [[ADD6]]
 // CHECK1-NEXT:    br i1 [[CMP7]], label [[OMP_INNER_FOR_BODY:%.*]], label [[OMP_INNER_FOR_END:%.*]]
 // CHECK1:       omp.inner.for.body:
-// CHECK1-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-NEXT:    [[TMP11:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
+// CHECK1-NEXT:    [[TMP11:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK1-NEXT:    [[MUL:%.*]] = mul i32 [[TMP11]], 1
 // CHECK1-NEXT:    [[ADD8:%.*]] = add i32 [[TMP10]], [[MUL]]
-// CHECK1-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-NEXT:    [[TMP12:%.*]] = load i32, ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4
+// CHECK1-NEXT:    [[TMP12:%.*]] = load i32, ptr [[I5]], align 4
 // CHECK1-NEXT:    [[IDXPROM:%.*]] = sext i32 [[TMP12]] to i64
 // CHECK1-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [10 x float], ptr @f, i64 0, i64 [[IDXPROM]]
-// CHECK1-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-NEXT:    call void @__captured_stmt(ptr [[I5]]), !llvm.access.group [[ACC_GRP3]]
+// CHECK1-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4
+// CHECK1-NEXT:    call void @__captured_stmt(ptr [[I5]])
 // CHECK1-NEXT:    br label [[OMP_BODY_CONTINUE:%.*]]
 // CHECK1:       omp.body.continue:
 // CHECK1-NEXT:    br label [[OMP_INNER_FOR_INC:%.*]]
 // CHECK1:       omp.inner.for.inc:
-// CHECK1-NEXT:    [[TMP13:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-NEXT:    [[TMP13:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK1-NEXT:    [[ADD9:%.*]] = add i32 [[TMP13]], 1
-// CHECK1-NEXT:    store i32 [[ADD9]], ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND]], !llvm.loop [[LOOP4:![0-9]+]]
+// CHECK1-NEXT:    store i32 [[ADD9]], ptr [[DOTOMP_IV]], align 4
+// CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND]], !llvm.loop [[LOOP3:![0-9]+]]
 // CHECK1:       omp.inner.for.end:
 // CHECK1-NEXT:    [[TMP14:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
 // CHECK1-NEXT:    [[TMP15:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_1]], align 4
@@ -645,31 +645,31 @@ void foo_simd(int low, int up) {
 // CHECK1-NEXT:    store i32 [[TMP27]], ptr [[DOTOMP_IV16]], align 4
 // CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND29:%.*]]
 // CHECK1:       omp.inner.for.cond29:
-// CHECK1-NEXT:    [[TMP28:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7:![0-9]+]]
-// CHECK1-NEXT:    [[TMP29:%.*]] = load i32, ptr [[DOTOMP_UB]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-NEXT:    [[TMP28:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
+// CHECK1-NEXT:    [[TMP29:%.*]] = load i32, ptr [[DOTOMP_UB]], align 4
 // CHECK1-NEXT:    [[ADD30:%.*]] = add i32 [[TMP29]], 1
 // CHECK1-NEXT:    [[CMP31:%.*]] = icmp ult i32 [[TMP28]], [[ADD30]]
 // CHECK1-NEXT:    br i1 [[CMP31]], label [[OMP_INNER_FOR_BODY32:%.*]], label [[OMP_INNER_FOR_END40:%.*]]
 // CHECK1:       omp.inner.for.body32:
-// CHECK1-NEXT:    [[TMP30:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_18]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-NEXT:    [[TMP31:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-NEXT:    [[TMP30:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_18]], align 4
+// CHECK1-NEXT:    [[TMP31:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
 // CHECK1-NEXT:    [[MUL33:%.*]] = mul i32 [[TMP31]], 1
 // CHECK1-NEXT:    [[ADD34:%.*]] = add i32 [[TMP30]], [[MUL33]]
-// CHECK1-NEXT:    store i32 [[ADD34]], ptr [[I28]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-NEXT:    [[TMP32:%.*]] = load i32, ptr [[I28]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-NEXT:    store i32 [[ADD34]], ptr [[I28]], align 4
+// CHECK1-NEXT:    [[TMP32:%.*]] = load i32, ptr [[I28]], align 4
 // CHECK1-NEXT:    [[IDXPROM35:%.*]] = sext i32 [[TMP32]] to i64
 // CHECK1-NEXT:    [[ARRAYIDX36:%.*]] = getelementptr inbounds [10 x float], ptr @f, i64 0, i64 [[IDXPROM35]]
-// CHECK1-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX36]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-NEXT:    call void @__captured_stmt.1(ptr [[I28]]), !llvm.access.group [[ACC_GRP7]]
+// CHECK1-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX36]], align 4
+// CHECK1-NEXT:    call void @__captured_stmt.1(ptr [[I28]])
 // CHECK1-NEXT:    br label [[OMP_BODY_CONTINUE37:%.*]]
 // CHECK1:       omp.body.continue37:
 // CHECK1-NEXT:    br label [[OMP_INNER_FOR_INC38:%.*]]
 // CHECK1:       omp.inner.for.inc38:
-// CHECK1-NEXT:    [[TMP33:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-NEXT:    [[TMP33:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
 // CHECK1-NEXT:    [[ADD39:%.*]] = add i32 [[TMP33]], 1
-// CHECK1-NEXT:    store i32 [[ADD39]], ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-NEXT:    call void @__kmpc_dispatch_fini_4u(ptr @[[GLOB1]], i32 [[TMP0]]), !llvm.access.group [[ACC_GRP7]]
-// CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND29]], !llvm.loop [[LOOP8:![0-9]+]]
+// CHECK1-NEXT:    store i32 [[ADD39]], ptr [[DOTOMP_IV16]], align 4
+// CHECK1-NEXT:    call void @__kmpc_dispatch_fini_4u(ptr @[[GLOB1]], i32 [[TMP0]])
+// CHECK1-NEXT:    br label [[OMP_INNER_FOR_COND29]], !llvm.loop [[LOOP5:![0-9]+]]
 // CHECK1:       omp.inner.for.end40:
 // CHECK1-NEXT:    br label [[OMP_DISPATCH_INC:%.*]]
 // CHECK1:       omp.dispatch.inc:
@@ -1201,32 +1201,32 @@ void foo_simd(int low, int up) {
 // CHECK1-IRBUILDER-NEXT:    store i32 0, ptr [[DOTOMP_IV]], align 4
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.cond:
-// CHECK1-IRBUILDER-NEXT:    [[TMP7:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3:![0-9]+]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP7:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[ADD6:%.*]] = add i32 [[TMP8]], 1
 // CHECK1-IRBUILDER-NEXT:    [[CMP7:%.*]] = icmp ult i32 [[TMP7]], [[ADD6]]
 // CHECK1-IRBUILDER-NEXT:    br i1 [[CMP7]], label [[OMP_INNER_FOR_BODY:%.*]], label [[OMP_INNER_FOR_END:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.body:
-// CHECK1-IRBUILDER-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[MUL:%.*]] = mul i32 [[TMP10]], 1
 // CHECK1-IRBUILDER-NEXT:    [[ADD8:%.*]] = add i32 [[TMP9]], [[MUL]]
-// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP11:%.*]] = load i32, ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP11:%.*]] = load i32, ptr [[I5]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[IDXPROM:%.*]] = sext i32 [[TMP11]] to i64
 // CHECK1-IRBUILDER-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [10 x float], ptr @f, i64 0, i64 [[IDXPROM]]
-// CHECK1-IRBUILDER-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-IRBUILDER-NEXT:    call void @__captured_stmt(ptr [[I5]]), !llvm.access.group [[ACC_GRP3]]
+// CHECK1-IRBUILDER-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4
+// CHECK1-IRBUILDER-NEXT:    call void @__captured_stmt(ptr [[I5]])
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_BODY_ORDERED_AFTER:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.body.ordered.after:
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_BODY_CONTINUE:%.*]]
 // CHECK1-IRBUILDER:       omp.body.continue:
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_INC:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.inc:
-// CHECK1-IRBUILDER-NEXT:    [[TMP12:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP12:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[ADD9:%.*]] = add i32 [[TMP12]], 1
-// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD9]], ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND]], !llvm.loop [[LOOP4:![0-9]+]]
+// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD9]], ptr [[DOTOMP_IV]], align 4
+// CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND]], !llvm.loop [[LOOP3:![0-9]+]]
 // CHECK1-IRBUILDER:       omp.inner.for.end:
 // CHECK1-IRBUILDER-NEXT:    [[TMP13:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[TMP14:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_1]], align 4
@@ -1278,34 +1278,34 @@ void foo_simd(int low, int up) {
 // CHECK1-IRBUILDER-NEXT:    store i32 [[TMP26]], ptr [[DOTOMP_IV16]], align 4
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND30:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.cond30:
-// CHECK1-IRBUILDER-NEXT:    [[TMP27:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7:![0-9]+]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP28:%.*]] = load i32, ptr [[DOTOMP_UB]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP27:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP28:%.*]] = load i32, ptr [[DOTOMP_UB]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[ADD31:%.*]] = add i32 [[TMP28]], 1
 // CHECK1-IRBUILDER-NEXT:    [[CMP32:%.*]] = icmp ult i32 [[TMP27]], [[ADD31]]
 // CHECK1-IRBUILDER-NEXT:    br i1 [[CMP32]], label [[OMP_INNER_FOR_BODY33:%.*]], label [[OMP_INNER_FOR_END42:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.body33:
-// CHECK1-IRBUILDER-NEXT:    [[TMP29:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_18]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP30:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP29:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_18]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP30:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[MUL34:%.*]] = mul i32 [[TMP30]], 1
 // CHECK1-IRBUILDER-NEXT:    [[ADD35:%.*]] = add i32 [[TMP29]], [[MUL34]]
-// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD35]], ptr [[I28]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-IRBUILDER-NEXT:    [[TMP31:%.*]] = load i32, ptr [[I28]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD35]], ptr [[I28]], align 4
+// CHECK1-IRBUILDER-NEXT:    [[TMP31:%.*]] = load i32, ptr [[I28]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[IDXPROM36:%.*]] = sext i32 [[TMP31]] to i64
 // CHECK1-IRBUILDER-NEXT:    [[ARRAYIDX37:%.*]] = getelementptr inbounds [10 x float], ptr @f, i64 0, i64 [[IDXPROM36]]
-// CHECK1-IRBUILDER-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX37]], align 4, !llvm.access.group [[ACC_GRP7]]
-// CHECK1-IRBUILDER-NEXT:    call void @__captured_stmt.1(ptr [[I28]]), !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX37]], align 4
+// CHECK1-IRBUILDER-NEXT:    call void @__captured_stmt.1(ptr [[I28]])
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_BODY33_ORDERED_AFTER:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.body33.ordered.after:
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_BODY_CONTINUE38:%.*]]
 // CHECK1-IRBUILDER:       omp.body.continue38:
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_INC39:%.*]]
 // CHECK1-IRBUILDER:       omp.inner.for.inc39:
-// CHECK1-IRBUILDER-NEXT:    [[TMP32:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    [[TMP32:%.*]] = load i32, ptr [[DOTOMP_IV16]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[ADD40:%.*]] = add i32 [[TMP32]], 1
-// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD40]], ptr [[DOTOMP_IV16]], align 4, !llvm.access.group [[ACC_GRP7]]
+// CHECK1-IRBUILDER-NEXT:    store i32 [[ADD40]], ptr [[DOTOMP_IV16]], align 4
 // CHECK1-IRBUILDER-NEXT:    [[OMP_GLOBAL_THREAD_NUM41:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB12]])
-// CHECK1-IRBUILDER-NEXT:    call void @__kmpc_dispatch_fini_4u(ptr @[[GLOB1]], i32 [[OMP_GLOBAL_THREAD_NUM41]]), !llvm.access.group [[ACC_GRP7]]
-// CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND30]], !llvm.loop [[LOOP8:![0-9]+]]
+// CHECK1-IRBUILDER-NEXT:    call void @__kmpc_dispatch_fini_4u(ptr @[[GLOB1]], i32 [[OMP_GLOBAL_THREAD_NUM41]])
+// CHECK1-IRBUILDER-NEXT:    br label [[OMP_INNER_FOR_COND30]], !llvm.loop [[LOOP5:![0-9]+]]
 // CHECK1-IRBUILDER:       omp.inner.for.end42:
 // CHECK1-IRBUILDER-NEXT:    br label [[OMP_DISPATCH_INC:%.*]]
 // CHECK1-IRBUILDER:       omp.dispatch.inc:
@@ -1812,30 +1812,30 @@ void foo_simd(int low, int up) {
 // CHECK3-NEXT:    store i32 0, ptr [[DOTOMP_IV]], align 4
 // CHECK3-NEXT:    br label [[OMP_INNER_FOR_COND:%.*]]
 // CHECK3:       omp.inner.for.cond:
-// CHECK3-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3:![0-9]+]]
-// CHECK3-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK3-NEXT:    [[TMP8:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
+// CHECK3-NEXT:    [[TMP9:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_2]], align 4
 // CHECK3-NEXT:    [[ADD6:%.*]] = add i32 [[TMP9]], 1
 // CHECK3-NEXT:    [[CMP7:%.*]] = icmp ult i32 [[TMP8]], [[ADD6]]
 // CHECK3-NEXT:    br i1 [[CMP7]], label [[OMP_INNER_FOR_BODY:%.*]], label [[OMP_INNER_FOR_END:%.*]]
 // CHECK3:       omp.inner.for.body:
-// CHECK3-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK3-NEXT:    [[TMP11:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK3-NEXT:    [[TMP10:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
+// CHECK3-NEXT:    [[TMP11:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK3-NEXT:    [[MUL:%.*]] = mul i32 [[TMP11]], 1
 // CHECK3-NEXT:    [[ADD8:%.*]] = add i32 [[TMP10]], [[MUL]]
-// CHECK3-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK3-NEXT:    [[TMP12:%.*]] = load i32, ptr [[I5]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK3-NEXT:    store i32 [[ADD8]], ptr [[I5]], align 4
+// CHECK3-NEXT:    [[TMP12:%.*]] = load i32, ptr [[I5]], align 4
 // CHECK3-NEXT:    [[IDXPROM:%.*]] = sext i32 [[TMP12]] to i64
 // CHECK3-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [10 x float], ptr @f, i64 0, i64 [[IDXPROM]]
-// CHECK3-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK3-NEXT:    call void @__captured_stmt(ptr [[I5]]), !llvm.access.group [[ACC_GRP3]]
+// CHECK3-NEXT:    store float 0.000000e+00, ptr [[ARRAYIDX]], align 4
+// CHECK3-NEXT:    call void @__captured_stmt(ptr [[I5]])
 // CHECK3-NEXT:    br label [[OMP_BODY_CONTINUE:%.*]]
 // CHECK3:       omp.body.continue:
 // CHECK3-NEXT:    br label [[OMP_INNER_FOR_INC:%.*]]
 // CHECK3:       omp.inner.for.inc:
-// CHECK3-NEXT:    [[TMP13:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
+// CHECK3-NEXT:    [[TMP13:%.*]] = load i32, ptr [[DOTOMP_IV]], align 4
 // CHECK3-NEXT:    [[ADD9:%.*]] = add i32 [[TMP13]], 1
-// CHECK3-NEXT:    store i32 [[ADD9]], ptr [[DOTOMP_IV]], align 4, !llvm.access.group [[ACC_GRP3]]
-// CHECK3-NEXT:    br label [...
[truncated]

github-actions · 2025-01-22T01:53:44Z

✅ With the latest revision this PR passed the C/C++ code formatter.

A proposed fix for llvm#95611 [OpenMP][SIMD] ordered has no effect in a loop SIMD region as of LLVM 18.1.0 Changes: - Implement new lowering behavior: Conservatively serialize "omp simd" loops that have `omp simd ordered` directive to prevent incorrect vectorization (which results in incorrect execution behavior of the miscompiled program). Implementation outline: - We start with the optimistic default initial value of `LoopStack.setParallel(/Enable=/true);` in `CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D)`. - We only disable the loop parallel memory access assumption with `if (HasOrderedDirective) LoopStack.setParallel(/Enable=/false);` using the `HasOrderedDirective` (which tests for the presence of an `OMPOrderedDirective`). - This results in no longer incorrectly vectorizing the loop when the `omp simd ordered` directive is present. Motivation: We'd like to prevent incorrect vectorization of the loops marked with the `#pragma omp ordered simd` directive which has previously resulted in miscompiled code. At the same time, we'd like the usage outside of the `#pragma omp ordered simd` context to remain unaffected: Note that in the test "clang/test/OpenMP/ordered_codegen.cpp" we only "lose" the `!llvm.access.group` metadata in `foo_simd` alone. This is a conservative, in that it's possible some of the loops would be possible to vectorize, but we prefer to avoid miscompilation of the loops that are currently illegal to vectorize. A concrete example follows: ```cpp // "test.c" #include <float.h> #include <math.h> #include <omp.h> #include <stdio.h> #include <stdlib.h> #include <time.h> int compare_float(float x1, float x2, float scalar) { const float diff = fabsf(x1 - x2); x1 = fabsf(x1); x2 = fabsf(x2); const float l = (x2 > x1) ? x2 : x1; if (diff <= l * scalar * FLT_EPSILON) return 1; else return 0; } #define ARRAY_SIZE 256 __attribute__((noinline)) void initialization_loop( float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) { const float max = 1000.0; srand(time(NULL)); for (int r = 0; r < ARRAY_SIZE; r++) { for (int c = 0; c < ARRAY_SIZE; c++) { X[r][c] = ((float)rand() / (float)(RAND_MAX)) * max; Y[r][c] = X[r][c]; } } } __attribute__((noinline)) void omp_simd_loop(float X[ARRAY_SIZE][ARRAY_SIZE]) { for (int r = 1; r < ARRAY_SIZE; ++r) { for (int c = 1; c < ARRAY_SIZE; ++c) { #pragma omp simd for (int k = 2; k < ARRAY_SIZE; ++k) { #pragma omp ordered simd X[r][k] = X[r][k - 2] + sinf((float)(r / c)); } } } } __attribute__((noinline)) int comparison_loop(float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) { int totalErrors_simd = 0; const float scalar = 1.0; for (int r = 1; r < ARRAY_SIZE; ++r) { for (int c = 1; c < ARRAY_SIZE; ++c) { for (int k = 2; k < ARRAY_SIZE; ++k) { Y[r][k] = Y[r][k - 2] + sinf((float)(r / c)); } } // check row for simd update for (int k = 0; k < ARRAY_SIZE; ++k) { if (!compare_float(X[r][k], Y[r][k], scalar)) { ++totalErrors_simd; } } } return totalErrors_simd; } int main(void) { float X[ARRAY_SIZE][ARRAY_SIZE]; float Y[ARRAY_SIZE][ARRAY_SIZE]; initialization_loop(X, Y); omp_simd_loop(X); const int totalErrors_simd = comparison_loop(X, Y); if (totalErrors_simd) { fprintf(stdout, "totalErrors_simd: %d \n", totalErrors_simd); fprintf(stdout, "%s : %d - FAIL: error in ordered simd computation.\n", __FILE__, __LINE__); } else { fprintf(stdout, "Success!\n"); } return totalErrors_simd; } ``` Before: ``` $ clang -fopenmp-simd -O3 -ffast-math -lm test.c -o test && ./test totalErrors_simd: 15408 test.c : 76 - FAIL: error in ordered simd computation. ``` clang 19.1.0: https://godbolt.org/z/6EvhxqEhe After: ``` $ clang -fopenmp-simd -O3 -ffast-math test.c -o test && ./test Success! ```

MattPD · 2025-02-04T04:06:32Z

@alexey-bataev Would you be able to take a look?

alexey-bataev

LG

MattPD · 2025-02-04T22:53:12Z

Thank you! Feel free to merge as I can't :-)

llvm-ci · 2025-02-06T14:56:20Z

LLVM Buildbot has detected a new failure on builder llvm-clang-x86_64-sie-ubuntu-fast running on sie-linux-worker while building clang at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/17521

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: OpenMP/simd_conservative_ordered.c' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 3: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -g0 -fopenmp-simd -x c -S -emit-llvm /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c -o - | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -g0 -fopenmp-simd -x c -S -emit-llvm /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c -o -
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c:5:10: fatal error: 'math.h' file not found
    5 | #include <math.h>
      |          ^~~~~~~~
1 error generated.
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck --allow-unused-prefixes /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/OpenMP/simd_conservative_ordered.c

--

********************

…ing" (#126079) Reverts #123867 to fix the test failures https://lab.llvm.org/buildbot/#/builders/144/builds/17521

alexey-bataev · 2025-02-06T15:05:16Z

clang/test/OpenMP/simd_conservative_ordered.c

@@ -0,0 +1,110 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --functions "omp_simd_loop" --check-globals smart --filter "access|\%omp.inner.for.cond.*\!llvm.loop"


Missed it, the clang tests cannot contain includes etc. Better to convert it to runtime test and put to libomp

Thanks; missed that, too!

I'm wondering what would be a good home for an OpenMP SIMD runtime test?
I think only

llvm-project/openmp/runtime/test/parallel/bug54082.c

Lines 34 to 36 in ec7167b

if (x != NULL) {

#pragma omp simd simdlen(16) aligned(x : 64)

for (int j = 0; j < N; j++) {

happens to exercise #pragma omp simd but that's still in the context of #pragma omp parallel and thus still in "openmp/runtime/test/parallel".
I suppose I could create "openmp/runtime/test/simd".

However, first I'm going to see if I can preserve the salient behavior of this test--i.e., the (non)emission of the llvm.access.group metadata--if I remove the headers and instead only manually provide the function prototypes. Perhaps that's going to be simpler.

Maybe test/misc_bugs?

All right, I've opened a PR #126172 with the updated test.

…ered" lowering" (#126079) Reverts llvm/llvm-project#123867 to fix the test failures https://lab.llvm.org/buildbot/#/builders/144/builds/17521

…m#123867) A proposed fix for llvm#95611 [OpenMP][SIMD] ordered has no effect in a loop SIMD region as of LLVM 18.1.0 Changes: - Implement new lowering behavior: Conservatively serialize "omp simd" loops that have `omp simd ordered` directive to prevent incorrect vectorization (which results in incorrect execution behavior of the miscompiled program). Implementation outline: - We start with the optimistic default initial value of `LoopStack.setParallel(/Enable=/true);` in `CodeGenFunction::EmitOMPSimdInit(const OMPLoopDirective &D)`. - We only disable the loop parallel memory access assumption with `if (HasOrderedDirective) LoopStack.setParallel(/Enable=/false);` using the `HasOrderedDirective` (which tests for the presence of an `OMPOrderedDirective`). - This results in no longer incorrectly vectorizing the loop when the `omp simd ordered` directive is present. Motivation: We'd like to prevent incorrect vectorization of the loops marked with the `#pragma omp ordered simd` directive which has previously resulted in miscompiled code. At the same time, we'd like the usage outside of the `#pragma omp ordered simd` context to remain unaffected: Note that in the test "clang/test/OpenMP/ordered_codegen.cpp" we only "lose" the `!llvm.access.group` metadata in `foo_simd` alone. This is conservative, in that it's possible some of the loops would be possible to vectorize, but we prefer to avoid miscompilation of the loops that are currently illegal to vectorize. A concrete example follows: ```cpp // "test.c" #include <float.h> #include <math.h> #include <omp.h> #include <stdio.h> #include <stdlib.h> #include <time.h> int compare_float(float x1, float x2, float scalar) { const float diff = fabsf(x1 - x2); x1 = fabsf(x1); x2 = fabsf(x2); const float l = (x2 > x1) ? x2 : x1; if (diff <= l * scalar * FLT_EPSILON) return 1; else return 0; } #define ARRAY_SIZE 256 __attribute__((noinline)) void initialization_loop( float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) { const float max = 1000.0; srand(time(NULL)); for (int r = 0; r < ARRAY_SIZE; r++) { for (int c = 0; c < ARRAY_SIZE; c++) { X[r][c] = ((float)rand() / (float)(RAND_MAX)) * max; Y[r][c] = X[r][c]; } } } __attribute__((noinline)) void omp_simd_loop(float X[ARRAY_SIZE][ARRAY_SIZE]) { for (int r = 1; r < ARRAY_SIZE; ++r) { for (int c = 1; c < ARRAY_SIZE; ++c) { #pragma omp simd for (int k = 2; k < ARRAY_SIZE; ++k) { #pragma omp ordered simd X[r][k] = X[r][k - 2] + sinf((float)(r / c)); } } } } __attribute__((noinline)) int comparison_loop(float X[ARRAY_SIZE][ARRAY_SIZE], float Y[ARRAY_SIZE][ARRAY_SIZE]) { int totalErrors_simd = 0; const float scalar = 1.0; for (int r = 1; r < ARRAY_SIZE; ++r) { for (int c = 1; c < ARRAY_SIZE; ++c) { for (int k = 2; k < ARRAY_SIZE; ++k) { Y[r][k] = Y[r][k - 2] + sinf((float)(r / c)); } } // check row for simd update for (int k = 0; k < ARRAY_SIZE; ++k) { if (!compare_float(X[r][k], Y[r][k], scalar)) { ++totalErrors_simd; } } } return totalErrors_simd; } int main(void) { float X[ARRAY_SIZE][ARRAY_SIZE]; float Y[ARRAY_SIZE][ARRAY_SIZE]; initialization_loop(X, Y); omp_simd_loop(X); const int totalErrors_simd = comparison_loop(X, Y); if (totalErrors_simd) { fprintf(stdout, "totalErrors_simd: %d \n", totalErrors_simd); fprintf(stdout, "%s : %d - FAIL: error in ordered simd computation.\n", __FILE__, __LINE__); } else { fprintf(stdout, "Success!\n"); } return totalErrors_simd; } ``` Before: ``` $ clang -fopenmp-simd -O3 -ffast-math -lm test.c -o test && ./test totalErrors_simd: 15408 test.c : 76 - FAIL: error in ordered simd computation. ``` clang 19.1.0: https://godbolt.org/z/6EvhxqEhe After: ``` $ clang -fopenmp-simd -O3 -ffast-math test.c -o test && ./test Success! ``` Co-authored-by: Matt P. Dziubinski <matt-p.dziubinski@hpe.com>

…ing" (llvm#126079) Reverts llvm#123867 to fix the test failures https://lab.llvm.org/buildbot/#/builders/144/builds/17521

llvmbot added clang Clang issues not falling into any other category clang:codegen IR generation bugs: mangling, exceptions, etc. clang:openmp OpenMP related changes to Clang labels Jan 22, 2025

MattPD mentioned this pull request Jan 22, 2025

[OpenMP][SIMD] ordered has no effect in a loop SIMD region as of LLVM 18.1.0 #95611

Closed

MattPD force-pushed the simd_conservative_ordered branch from 1b603f7 to f02e20d Compare January 22, 2025 20:02

MattPD force-pushed the simd_conservative_ordered branch from f02e20d to b69344c Compare January 23, 2025 00:56

alexey-bataev approved these changes Feb 4, 2025

View reviewed changes

alexey-bataev merged commit 60d8e6f into llvm:main Feb 6, 2025
8 checks passed

alexey-bataev mentioned this pull request Feb 6, 2025

Revert "[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering" #126079

Merged

alexey-bataev added a commit that referenced this pull request Feb 6, 2025

Revert "[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lower…

3041dd5

…ing" (#126079) Reverts #123867 to fix the test failures https://lab.llvm.org/buildbot/#/builders/144/builds/17521

alexey-bataev reviewed Feb 6, 2025

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[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering #123867

[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering #123867

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MattPD commented Jan 22, 2025 •

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MattPD Feb 6, 2025 •

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		@@ -0,0 +1,110 @@
		// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --functions "omp_simd_loop" --check-globals smart --filter "access\|\%omp.inner.for.cond.*\!llvm.loop"

	if (x != NULL) {
	#pragma omp simd simdlen(16) aligned(x : 64)
	for (int j = 0; j < N; j++) {

[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering #123867

[OpenMP][SIMD][FIX] Use conservative "omp simd ordered" lowering #123867

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