[llvm] 92e0fb0 - [DebugInfo][LoopUnroll] Preserve DebugLocs on optimized cond branches (#114225)

[via llvm-commits]

Author: Stephen Tozer
Date: 2024-11-08T16:52:30Z
New Revision: 92e0fb0c944254312d7b9c6ca64a026643617f60

URL: https://github.com/llvm/llvm-project/commit/92e0fb0c944254312d7b9c6ca64a026643617f60
DIFF: https://github.com/llvm/llvm-project/commit/92e0fb0c944254312d7b9c6ca64a026643617f60.diff

LOG: [DebugInfo][LoopUnroll] Preserve DebugLocs on optimized cond branches (#114225)

This patch fixes a simple error where as part of loop unrolling we
optimize conditional loop-exiting branches into unconditional branches
when we know that they will or won't exit the loop, but does not
propagate the source location of the original branch to the new one.

Found using https://github.com/llvm/llvm-project/pull/107279.

Added: 
    llvm/test/Transforms/LoopUnroll/preserve-branch-debuglocs.ll

Modified: 
    llvm/lib/Transforms/Utils/LoopUnroll.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index ad5670ae331765..85d4415970a00a 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -880,7 +880,8 @@ llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
     DeadSucc->removePredecessor(Src, /* KeepOneInputPHIs */ true);
 
     // Replace the conditional branch with an unconditional one.
-    BranchInst::Create(Dest, Term->getIterator());
+    auto *BI = BranchInst::Create(Dest, Term->getIterator());
+    BI->setDebugLoc(Term->getDebugLoc());
     Term->eraseFromParent();
 
     DTUpdates.emplace_back(DominatorTree::Delete, Src, DeadSucc);

diff  --git a/llvm/test/Transforms/LoopUnroll/preserve-branch-debuglocs.ll b/llvm/test/Transforms/LoopUnroll/preserve-branch-debuglocs.ll
new file mode 100644
index 00000000000000..623fb68c784fe7
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/preserve-branch-debuglocs.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 5
+; RUN: opt < %s -passes=loop-unroll -S | FileCheck %s
+; RUN: opt < %s -passes=loop-unroll-full -S | FileCheck %s
+
+;; Loop Unrolling should preserve the DebugLocs of conditional branches that get
+;; optimized into unconditional branches.
+
+define i32 @_ZeqRK4int3S1_() {
+; CHECK-LABEL: define i32 @_ZeqRK4int3S1_() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_BODY:.*]]
+; CHECK:       [[FOR_COND:.*]]:
+; CHECK-NEXT:    br label %[[CLEANUP:.*]], !dbg [[DBG3:![0-9]+]]
+; CHECK:       [[FOR_BODY]]:
+; CHECK-NEXT:    br i1 false, label %[[FOR_COND]], label %[[CLEANUP]]
+; CHECK:       [[CLEANUP]]:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  br label %for.body
+
+for.cond:                                         ; preds = %for.body
+  br i1 false, label %cleanup, label %for.body, !dbg !3
+
+for.body:                                         ; preds = %for.cond, %entry
+  br i1 false, label %for.cond, label %cleanup
+
+cleanup:                                          ; preds = %for.body, %for.cond
+  ret i32 0
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 20.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug)
+!1 = !DIFile(filename: "test.cpp", directory: "/tmp")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DILocation(line: 304, column: 2, scope: !4)
+!4 = distinct !DILexicalBlock(scope: !5, file: !1, line: 304, column: 2)
+!5 = distinct !DISubprogram(name: "operator==", linkageName: "_ZeqRK4int3S1_", scope: !1, file: !1, line: 302, type: !6, scopeLine: 303, spFlags: DISPFlagDefinition, unit: !0)
+!6 = distinct !DISubroutineType(types: !7)
+!7 = !{}
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug)
+; CHECK: [[META1]] = !DIFile(filename: "test.cpp", directory: {{.*}})
+; CHECK: [[META2:![0-9]+]] = !{i32 2, !"Debug Info Version", i32 3}
+; CHECK: [[DBG3]] = !DILocation(line: 304, column: 2, scope: [[META4:![0-9]+]])
+; CHECK: [[META4]] = distinct !DILexicalBlock(scope: [[META5:![0-9]+]], file: [[META1]], line: 304, column: 2)
+; CHECK: [[META5]] = distinct !DISubprogram(name: "operator==", linkageName: "_ZeqRK4int3S1_", scope: [[META1]], file: [[META1]], line: 302, type: [[META6:![0-9]+]], scopeLine: 303, spFlags: DISPFlagDefinition, unit: [[META0]])
+; CHECK: [[META6]] = distinct !DISubroutineType(types: [[META7:![0-9]+]])
+; CHECK: [[META7]] = !{}
+;.