[MLIR][LLVM] CallSiteLoc without caller scope not translatable

[zyx-billy]

If a CallSiteLoc's caller cannot be translated (returns null), we cannot simply return the translation of the callee location. This is because the resulting DILocation will not have any InlinedAt field for the function it is in, and will fail the LLVM IR verifier.

---

Example:

This situation occurs when we have a nested callsite loc, where the middle function in the stack does not have a debug scope

func A {
  foo loc(fused<#A>["a":1:1])
}
func B {
  call @A loc("b":1:1)
}
func C {
  call @B loc(fused<#C>["c":1:1])
}

When A is inlined into B, and B is inlined into C, we get

func C {
  foo loc(callsite(
            callsite(fused<#A>["a":1:1] at loc("b":1:1))
           at
            fused<#C>["c":1:1]))
}

We do not want to translate this into just a !DILocation(line: 1, column: 1, scope: !A), as that would not be legal in func C, so this is not something we can represent in LLVM IR.

[llvmbot]

@llvm/pr-subscribers-mlir-llvm

@llvm/pr-subscribers-mlir

Author: Billy Zhu (zyx-billy)

Changes

If a CallSiteLoc's caller cannot be translated (returns null), we cannot simply return the translation of the callee location. This is because the resulting DILocation will not have any InlinedAt field for the function it is in, and will fail the LLVM IR verifier.

---

Example:

This situation occurs when we have a nested callsite loc, where the middle function in the stack does not have a debug scope

func A {
  foo loc(fused<#A>["a":1:1])
}
func B {
  call @<!-- -->A loc("b":1:1)
}
func C {
  call @<!-- -->B loc(fused&lt;#C&gt;["c":1:1])
}

When A is inlined into B, and B is inlined into C, we get

func C {
  foo loc(callsite(
            callsite(fused<#A>["a":1:1] at loc("b":1:1))
           at
            fused<#C>["c":1:1]))
}

We do not want to translate this into just a !DILocation(line: 1, column: 1, scope: !A), as that would not be legal in func C, so this is not something we can represent in LLVM IR.

---

Full diff: https://github.com/llvm/llvm-project/pull/90759.diff

2 Files Affected:

• (modified) mlir/lib/Target/LLVMIR/DebugTranslation.cpp (+4)
• (modified) mlir/test/Target/LLVMIR/llvmir-debug.mlir (+6-3)

diff --git a/mlir/lib/Target/LLVMIR/DebugTranslation.cpp b/mlir/lib/Target/LLVMIR/DebugTranslation.cpp
index 2de5e372d88c0e..f02939abc5fe18 100644
--- a/mlir/lib/Target/LLVMIR/DebugTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/DebugTranslation.cpp
@@ -406,6 +406,10 @@ llvm::DILocation *DebugTranslation::translateLoc(Location loc,
   if (auto callLoc = dyn_cast<CallSiteLoc>(loc)) {
     // For callsites, the caller is fed as the inlinedAt for the callee.
     auto *callerLoc = translateLoc(callLoc.getCaller(), scope, inlinedAt);
+    // If the caller scope does not exist, the callsite cannot be represented
+    // in LLVM (the callee scope may not match the function it is in).
+    if (!callerLoc)
+      return nullptr;
     llvmLoc = translateLoc(callLoc.getCallee(), nullptr, callerLoc);
     // Fallback: Ignore callee if it has no debug scope.
     if (!llvmLoc)
diff --git a/mlir/test/Target/LLVMIR/llvmir-debug.mlir b/mlir/test/Target/LLVMIR/llvmir-debug.mlir
index 8ab1a1b290dad3..e8a3d65209afde 100644
--- a/mlir/test/Target/LLVMIR/llvmir-debug.mlir
+++ b/mlir/test/Target/LLVMIR/llvmir-debug.mlir
@@ -108,12 +108,15 @@ llvm.func @func_with_debug(%arg: i64) {
   // CHECK: call void @func_no_debug(), !dbg ![[NAMED_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc("named"("foo.mlir":10:10))
 
-  // CHECK: call void @func_no_debug(), !dbg ![[CALLSITE_LOC:[0-9]+]]
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc(callsite("nodebug.cc":3:4 at "mysource.cc":5:6))
 
-  // CHECK: call void @func_no_debug(), !dbg ![[CALLSITE_LOC:[0-9]+]]
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC]]
   llvm.call @func_no_debug() : () -> () loc(callsite("nodebug.cc":3:4 at fused<#sp0>["mysource.cc":5:6]))
 
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC]]
+  llvm.call @func_no_debug() : () -> () loc(callsite(callsite(fused<#callee>["nodebug.cc":3:4] at "foo.mlir":2:4) at fused<#sp0>["mysource.cc":5:6]))
+
   // CHECK: call void @func_no_debug(), !dbg ![[FUSED_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc(fused[callsite(fused<#callee>["mysource.cc":5:6] at "mysource.cc":1:1), "mysource.cc":1:1])
 
@@ -153,7 +156,7 @@ llvm.func @empty_types() {
 // CHECK: ![[BLOCK_LOC]] = distinct !DILexicalBlock(scope: ![[FUNC_LOC]])
 // CHECK: ![[NO_NAME_VAR]] = !DILocalVariable(scope: ![[BLOCK_LOC]])
 
-// CHECK-DAG: ![[CALLSITE_LOC]] = !DILocation(line: 5, column: 6,
+// CHECK-DAG: ![[MY_SOURCE_LOC]] = !DILocation(line: 5, column: 6
 // CHECK-DAG: ![[FILE_LOC]] = !DILocation(line: 1, column: 2,
 // CHECK-DAG: ![[NAMED_LOC]] = !DILocation(line: 10, column: 10
 // CHECK-DAG: ![[FUSED_LOC]] = !DILocation(line: 1, column: 1

[gysit]

LGTM

Thanks for fixing!