[AggrInstCombine][DebugInfo] Propagate DILocation for inlined memchr

[SLTozer]

When AggressiveInstCombine replaces a memchr with a switch instruction, it currently drops the DILocation for that memchr. This patch changes this, propagating the memchr DILocation to all the generated instructions that replace it.

Found using #107279.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Stephen Tozer (SLTozer)

Changes

When AggressiveInstCombine replaces a memchr with a switch instruction, it currently drops the DILocation for that memchr. This patch changes this, propagating the memchr DILocation to all the generated instructions that replace it.

Found using #107279.

---

Full diff: https://github.com/llvm/llvm-project/pull/134808.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp (+1)
• (added) llvm/test/Transforms/AggressiveInstCombine/dbgloc-memchr.ll (+44)

diff --git a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
index 6b0f568864fd5..af994022a8ec1 100644
--- a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
+++ b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
@@ -1133,6 +1133,7 @@ static bool foldMemChr(CallInst *Call, DomTreeUpdater *DTU,
   BasicBlock *BB = Call->getParent();
   BasicBlock *BBNext = SplitBlock(BB, Call, DTU);
   IRBuilder<> IRB(BB);
+  IRB.SetCurrentDebugLocation(Call->getDebugLoc());
   IntegerType *ByteTy = IRB.getInt8Ty();
   BB->getTerminator()->eraseFromParent();
   SwitchInst *SI = IRB.CreateSwitch(
diff --git a/llvm/test/Transforms/AggressiveInstCombine/dbgloc-memchr.ll b/llvm/test/Transforms/AggressiveInstCombine/dbgloc-memchr.ll
new file mode 100644
index 0000000000000..c580490a9ae68
--- /dev/null
+++ b/llvm/test/Transforms/AggressiveInstCombine/dbgloc-memchr.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -p=aggressive-instcombine < %s | FileCheck %s
+;; Tests that when we inline a simple memchr, we transfer its DILocation to the
+;; generated instructions.
+
+@.str.30 = constant [3 x i8] c"/\\\00"
+
+define i32 @foo(i32 %conv22) {
+; CHECK-LABEL: define i32 @foo(
+; CHECK-SAME: i32 [[CONV22:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i32 [[CONV22]] to i8, !dbg [[DBG3:![0-9]+]]
+; CHECK-NEXT:    switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
+; CHECK-NEXT:    ], !dbg [[DBG3]]
+; CHECK:       [[MEMCHR_SUCCESS:.*:]]
+; CHECK-NEXT:    br label %[[ENTRY_SPLIT]], !dbg [[DBG3]]
+; CHECK:       [[ENTRY_SPLIT]]:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %memchr = call ptr @memchr(ptr @.str.30, i32 %conv22, i64 0), !dbg !3
+  ret i32 0
+}
+
+declare ptr @memchr(ptr, i32, i64)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 20.0.0git")
+!1 = !DIFile(filename: "test.c", directory: "/tmp")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DILocation(line: 19, column: 42, scope: !4)
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 174, type: !5, unit: !0, retainedNodes: !6)
+!5 = !DISubroutineType(types: !6)
+!6 = !{}
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C11, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug)
+; CHECK: [[META1]] = !DIFile(filename: "test.c", directory: {{.*}})
+; CHECK: [[DBG3]] = !DILocation(line: 19, column: 42, scope: [[META4:![0-9]+]])
+; CHECK: [[META4]] = distinct !DISubprogram(name: "foo", scope: [[META1]], file: [[META1]], line: 174, type: [[META5:![0-9]+]], spFlags: DISPFlagDefinition, unit: [[META0]], retainedNodes: [[META6:![0-9]+]])
+; CHECK: [[META5]] = !DISubroutineType(types: [[META6]])
+; CHECK: [[META6]] = !{}
+;.

[OCHyams]

LGTM, follows the same rules as inlining nodbg function IIRC (propagate call loc)