[DebugInfo][Inline] Propagate source locs when simplifying cond branches

[SLTozer]

During inlining, we may opportunistically simplify conditional branches (incl. switches) to unconditional branches if, after inlining, their destination is fixed. While we do this, we should propagate any DILocation attached to the original branch to the simplified branch, which this patch enables.

Found using #107279.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-debuginfo

Author: Stephen Tozer (SLTozer)

Changes

During inlining, we may opportunistically simplify conditional branches (incl. switches) to unconditional branches if, after inlining, their destination is fixed. While we do this, we should propagate any DILocation attached to the original branch to the simplified branch, which this patch enables.

Found using #107279.

---

Full diff: https://github.com/llvm/llvm-project/pull/134827.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Utils/CloneFunction.cpp (+6-2)
• (added) llvm/test/Transforms/Inline/X86/inline-simplified-branch-dbg-loc.ll (+97)

diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 9387797019023..35550642a4365 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -607,7 +607,9 @@ void PruningFunctionCloner::CloneBlock(
       // Constant fold to uncond branch!
       if (Cond) {
         BasicBlock *Dest = BI->getSuccessor(!Cond->getZExtValue());
-        VMap[OldTI] = BranchInst::Create(Dest, NewBB);
+        auto *NewBI = BranchInst::Create(Dest, NewBB);
+        NewBI->setDebugLoc(BI->getDebugLoc());
+        VMap[OldTI] = NewBI;
         ToClone.push_back(Dest);
         TerminatorDone = true;
       }
@@ -622,7 +624,9 @@ void PruningFunctionCloner::CloneBlock(
     if (Cond) { // Constant fold to uncond branch!
       SwitchInst::ConstCaseHandle Case = *SI->findCaseValue(Cond);
       BasicBlock *Dest = const_cast<BasicBlock *>(Case.getCaseSuccessor());
-      VMap[OldTI] = BranchInst::Create(Dest, NewBB);
+      auto *NewBI = BranchInst::Create(Dest, NewBB);
+      NewBI->setDebugLoc(SI->getDebugLoc());
+      VMap[OldTI] = NewBI;
       ToClone.push_back(Dest);
       TerminatorDone = true;
     }
diff --git a/llvm/test/Transforms/Inline/X86/inline-simplified-branch-dbg-loc.ll b/llvm/test/Transforms/Inline/X86/inline-simplified-branch-dbg-loc.ll
new file mode 100644
index 0000000000000..98844a753840a
--- /dev/null
+++ b/llvm/test/Transforms/Inline/X86/inline-simplified-branch-dbg-loc.ll
@@ -0,0 +1,97 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -mtriple=x86_64-unknown-unknown -S -passes=inline | FileCheck %s
+
+;; Test that when we simplify inlined conditional branch/switch instructions to
+;; unconditional branches, we propagate the original branch's source location to
+;; the simplified branch.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i1 @ham() {
+; CHECK-LABEL: define i1 @ham() {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    br i1 poison, label %[[BB1_I:.*]], label %[[HOGE_EXIT:.*]]
+; CHECK:       [[BB1_I]]:
+; CHECK-NEXT:    br label %[[HOGE_EXIT]], !dbg [[DBG4:![0-9]+]]
+; CHECK:       [[HOGE_EXIT]]:
+; CHECK-NEXT:    br i1 poison, label %[[BB1_I1:.*]], label %[[QUUX_EXIT:.*]]
+; CHECK:       [[BB1_I1]]:
+; CHECK-NEXT:    br label %[[QUUX_EXIT]], !dbg [[DBG7:![0-9]+]]
+; CHECK:       [[QUUX_EXIT]]:
+; CHECK-NEXT:    ret i1 false
+;
+bb:
+  %call1 = call fastcc i32 @hoge(i1 false)
+  %call2 = call fastcc i32 @quux(i8 0)
+  ret i1 false
+}
+
+define fastcc i32 @hoge(i1 %in) {
+; CHECK-LABEL: define fastcc i32 @hoge(
+; CHECK-SAME: i1 [[IN:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    br i1 poison, label %[[BB1:.*]], label %[[BB2:.*]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br i1 [[IN]], label %[[BB2]], label %[[BB2]], !dbg [[DBG4]]
+; CHECK:       [[BB2]]:
+; CHECK-NEXT:    ret i32 0
+;
+bb:
+  br i1 poison, label %bb1, label %bb2
+
+bb1:                                              ; preds = %bb
+  br i1 %in, label %bb2, label %bb2, !dbg !4
+
+bb2:                                              ; preds = %bb1, %bb1, %bb
+  ret i32 0
+}
+
+define fastcc i32 @quux(i8 %in) {
+; CHECK-LABEL: define fastcc i32 @quux(
+; CHECK-SAME: i8 [[IN:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    br i1 poison, label %[[BB1:.*]], label %[[BB2:.*]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    switch i8 [[IN]], label %[[BB2]] [
+; CHECK-NEXT:      i8 0, label %[[BB2]]
+; CHECK-NEXT:    ], !dbg [[DBG7]]
+; CHECK:       [[BB2]]:
+; CHECK-NEXT:    ret i32 0
+;
+bb:
+  br i1 poison, label %bb1, label %bb2
+
+bb1:                                              ; preds = %bb
+  switch i8 %in, label %bb2 [
+  i8 0, label %bb2
+  ], !dbg !14
+
+
+bb2:                                              ; preds = %bb1, %bb1, %bb
+  ret i32 0
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 20.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2, globals: !2, imports: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "inline-simplified-branch-dbg-loc.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocation(line: 26, column: 11, scope: !12)
+!6 = !DIFile(filename: "inline-simplified-branch-dbg-loc.cpp", directory: "/tmp")
+!12 = distinct !DISubprogram(name: "hoge", linkageName: "hoge", scope: !6, file: !6, line: 10, type: !13, scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!13 = distinct !DISubroutineType(types: !2)
+!14 = !DILocation(line: 16, column: 1, scope: !15)
+!15 = distinct !DISubprogram(name: "quux", linkageName: "quux", scope: !6, file: !6, line: 20, type: !13, scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: [[META2:![0-9]+]], globals: [[META2]], imports: [[META2]], splitDebugInlining: false, nameTableKind: None)
+; CHECK: [[META1]] = !DIFile(filename: "inline-simplified-branch-dbg-loc.cpp", directory: {{.*}})
+; CHECK: [[META2]] = !{}
+; CHECK: [[DBG4]] = !DILocation(line: 26, column: 11, scope: [[META5:![0-9]+]])
+; CHECK: [[META5]] = distinct !DISubprogram(name: "hoge", linkageName: "hoge", scope: [[META1]], file: [[META1]], line: 10, type: [[META6:![0-9]+]], scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META2]])
+; CHECK: [[META6]] = distinct !DISubroutineType(types: [[META2]])
+; CHECK: [[DBG7]] = !DILocation(line: 16, column: 1, scope: [[META8:![0-9]+]])
+; CHECK: [[META8]] = distinct !DISubprogram(name: "quux", linkageName: "quux", scope: [[META1]], file: [[META1]], line: 20, type: [[META6]], scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META2]])
+;.

[OCHyams]

LGTM