[InstCombine] Improve coverage of foldSelectValueEquivalence for non-constants
#94719
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@llvm/pr-subscribers-llvm-transforms Author: None (goldsteinn) Changes
Full diff: https://github.com/llvm/llvm-project/pull/94719.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index b04e0b300f95a..dc0e7a032198b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1300,6 +1300,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
if (TrueVal == OldOp)
return nullptr;
+ bool NewOpNeverUndef = false;
+
if (Value *V = simplifyWithOpReplaced(TrueVal, OldOp, NewOp, SQ,
/* AllowRefinement=*/true)) {
// Need some guarantees about the new simplified op to ensure we don't inf
@@ -1309,12 +1311,51 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
isGuaranteedNotToBeUndef(V, SQ.AC, &Sel, &DT))
return replaceOperand(Sel, Swapped ? 2 : 1, V);
- // If NewOp is a constant and OldOp is not replace iff NewOp doesn't
- // contain and undef elements.
- if (match(NewOp, m_ImmConstant())) {
- if (isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
- return replaceOperand(Sel, Swapped ? 2 : 1, V);
+ // We can't do any further replacement if NewOp may be undef.
+ if (!isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
return nullptr;
+
+ // If NewOp is a constant, replace.
+ if (match(NewOp, m_ImmConstant()))
+ return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+ // If we simplified the TrueArm -> NewOp then replace.
+ // This handles things like `select`/`min`/`max`/`or`/`and`/etc...
+ if (NewOp == V)
+ return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+ NewOpNeverUndef = true;
+ }
+
+ // If we can't simplify, but we will either:
+ // 1) Create a new binop where both ops are NewOp i.e (add x, y) is "worse"
+ // than (add y, y) in this case, wait until the second call so we don't
+ // miss a one-use simplification.
+ // 2) Create a new one-use instruction.
+ // proceed.
+ if (TrueVal->hasOneUse() && isa<Instruction>(TrueVal)) {
+ bool BinOpMatch =
+ match(TrueVal, m_c_BinOp(m_Specific(OldOp), m_Specific(NewOp)));
+ bool NewOneUse = isa<Instruction>(OldOp) && OldOp->hasNUses(2) &&
+ (!isa<Instruction>(NewOp) || !NewOp->hasOneUse());
+ if (BinOpMatch || NewOneUse) {
+ bool Replaced = false;
+ auto *TrueIns = cast<Instruction>(TrueVal);
+ for (unsigned OpIdx = 0; OpIdx < TrueIns->getNumOperands(); ++OpIdx) {
+ if (TrueIns->getOperand(OpIdx) != OldOp)
+ continue;
+ // Need to ensure NewOp is noundef (same reason as above). Wait
+ // until the last moment to do this check as it can be relatively
+ // expensive.
+ if (!NewOpNeverUndef &&
+ !isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
+ break;
+ NewOpNeverUndef = true;
+ TrueIns->setOperand(OpIdx, NewOp);
+ Replaced = true;
+ }
+ if (Replaced)
+ return replaceOperand(Sel, Swapped ? 2 : 1, TrueIns);
}
}
@@ -1327,7 +1368,7 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
// FIXME: Support vectors.
if (OldOp == CmpLHS && match(NewOp, m_ImmConstant()) &&
!match(OldOp, m_ImmConstant()) && !Cmp.getType()->isVectorTy() &&
- isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
+ (NewOpNeverUndef || isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT)))
if (replaceInInstruction(TrueVal, OldOp, NewOp))
return &Sel;
return nullptr;
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
new file mode 100644
index 0000000000000..d2a5c71025370
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
@@ -0,0 +1,184 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare void @use.i1(i1)
+declare void @use.i8(i8)
+define i8 @replace_with_y_noundef(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_noundef(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Y]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %and = and i8 %x, %y
+ %sel = select i1 %cmp, i8 %and, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_noundef(i8 noundef %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_x_noundef(
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: call void @use.i1(i1 [[CMP]])
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[X]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp ne i8 %x, %y
+ call void @use.i1(i1 %cmp)
+ %and = or i8 %x, %y
+ %sel = select i1 %cmp, i8 %z, i8 %and
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_maybe_undef_fail(i8 %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_x_maybe_undef_fail(
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: call void @use.i1(i1 [[CMP]])
+; CHECK-NEXT: [[AND:%.*]] = or i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[AND]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp ne i8 %x, %y
+ call void @use.i1(i1 %cmp)
+ %and = or i8 %x, %y
+ %sel = select i1 %cmp, i8 %z, i8 %and
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_new_oneuse(i8 noundef %xx, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_new_oneuse(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = shl nuw i8 [[Y]], 1
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %add = add nuw i8 %x, %y
+ %sel = select i1 %cmp, i8 %add, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_new_oneuse2(i8 %xx, i8 noundef %y, i8 %z, i8 %q) {
+; CHECK-LABEL: @replace_with_y_for_new_oneuse2(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[Y]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %add = add nuw i8 %x, %q
+ %sel = select i1 %cmp, i8 %add, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_new_oneuse(i8 noundef %xx, i8 noundef %yy, i8 %z, i8 %w) {
+; CHECK-LABEL: @replace_with_x_for_new_oneuse(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[X]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_new_oneuse2(i8 noundef %xx, i8 %yy, i8 %z, i8 %w, i8 %q) {
+; CHECK-LABEL: @replace_with_x_for_new_oneuse2(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[Y]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %q, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_simple_binop(i8 noundef %xx, i8 %yy, i8 %z, i8 %w) {
+; CHECK-LABEL: @replace_with_x_for_simple_binop(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[X]]
+; CHECK-NEXT: call void @use.i8(i8 [[Y]])
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ call void @use.i8(i8 %y)
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_none_for_new_oneuse_fail_maybe_undef(i8 %xx, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_none_for_new_oneuse_fail_maybe_undef(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[Y]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop_fail_multiuse(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop_fail_multiuse(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: call void @use.i8(i8 [[MUL]])
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ call void @use.i8(i8 %mul)
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop_fail(i8 %x, i8 noundef %y, i8 %z, i8 %q) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop_fail(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %q
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
|
goldsteinn
changed the title
foldSelectValueEquivalence for non-constants
|
Going to run csmith for a few days w/ this. Will ping back results probably monday. |
nikic
requested changes
Jun 7, 2024
Is the second half so complicated? I guess I can yet again split it too a knew PR so we can test it. Regarding Think the following constraints make it pretty trivially impossible.
Although the more I think about, the more I think it can't lead to inf loop. |
|
Ran ~5million csmith tests. No inf loops or bad codegen. Although note only got different resulting IR ~100 times over all the tests. |
dtcxzyw
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Jun 12, 2024
I agree. |
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Dropped the use-reduction code. Think for this to inf loop you would need to violate SSA i.e: f(x, y) -> y -> y(x, z) -> x. For us to go from x -> y, then y would need to both be dominated by x and dominate x. |
nikic
reviewed
Jun 22, 2024
…n-constants If f(Y) simplifies to Y, replace with Y. This requires Y to be non-undef.
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AlexisPerry
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…n-constants If f(Y) simplifies to Y, replace with Y. This requires Y to be non-undef. Closes llvm#94719
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foldSelectValueEquivalence; NFCfoldSelectValueEquivalencefor non-constantsThere are a few more cases we can easily cover.
These all require that Y is not undef