[llvm] [JumpThreading][DebugInfo] Propagate DebugLocs when simplifying loads (PR #157683)
Stephen Tozer via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 10 05:17:35 PDT 2025
https://github.com/SLTozer updated https://github.com/llvm/llvm-project/pull/157683
>From a5b9ff5977b079fe3585b2978068d6bfe1aeee6f Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Tue, 9 Sep 2025 15:37:57 +0100
Subject: [PATCH] [JumpThreading][DebugInfo] Propagate DebugLocs when
simplifying loads
In simplifyPartiallyRedundantLoad we may replace a load with a PHI of
available values in predecessor blocks. As part of this process, we may
need to cast those values, which we do by inserting a new cast at the
end of the predecessor. These cast instructions should take their debug
location from the load instruction, just as the PHI does; we make an
exception if the predecessor does not unconditionally branch to the load's
block, as in that case we are not guaranteed to reach the load and must
therefore drop its debug location.
---
llvm/lib/Transforms/Scalar/JumpThreading.cpp | 11 ++-
...plify-partially-redundant-load-debugloc.ll | 88 +++++++++++++++++++
2 files changed, 98 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/Transforms/JumpThreading/simplify-partially-redundant-load-debugloc.ll
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index c2a737d8f9a4a..c7d71eb5633ec 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1437,9 +1437,18 @@ bool JumpThreadingPass::simplifyPartiallyRedundantLoad(LoadInst *LoadI) {
// AvailablePreds vector as we go so that all of the PHI entries for this
// predecessor use the same bitcast.
Value *&PredV = I->second;
- if (PredV->getType() != LoadI->getType())
+ if (PredV->getType() != LoadI->getType()) {
PredV = CastInst::CreateBitOrPointerCast(
PredV, LoadI->getType(), "", P->getTerminator()->getIterator());
+ // The new cast is producing the value used to replace the load
+ // instruction, so uses the load's debug location. If P does not always
+ // branch to the load BB however then the debug location must be dropped,
+ // as it is hoisted past a conditional branch.
+ DebugLoc DL = P->getTerminator()->getNumSuccessors() == 1
+ ? LoadI->getDebugLoc()
+ : DebugLoc::getDropped();
+ cast<CastInst>(PredV)->setDebugLoc(DL);
+ }
PN->addIncoming(PredV, I->first);
}
diff --git a/llvm/test/Transforms/JumpThreading/simplify-partially-redundant-load-debugloc.ll b/llvm/test/Transforms/JumpThreading/simplify-partially-redundant-load-debugloc.ll
new file mode 100644
index 0000000000000..80f7a53d5e2a3
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/simplify-partially-redundant-load-debugloc.ll
@@ -0,0 +1,88 @@
+; RUN: opt -S -passes=jump-threading < %s | FileCheck %s
+
+;; Check that when we simplify the load of %p by replacing it with 0 when coming
+;; from %left, the inttoptr cast instruction is assigned the DILocation from the
+;; load instruction.
+
+; CHECK-LABEL: define void @foo(
+
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[P:%.*]] = alloca i32, align 8
+; CHECK-NEXT: br i1 {{.*}}, label %[[LEFT:.*]], label %[[RIGHT:.*]]
+
+;; Cast in "left" should have the load's debug location.
+; CHECK: [[LEFT]]:
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr [[P]], i8 0, i64 8, i1 false)
+; CHECK-NEXT: [[TMP0:%.*]] = inttoptr i64 0 to ptr, !dbg [[LOAD_LOC:![0-9]+]]
+; CHECK-NEXT: br label %[[END:.*]]
+
+; CHECK: [[RIGHT]]:
+; CHECK-NEXT: br i1 {{.*}}, label %[[RIGHT_LEFT:.*]], label %[[ENDTHREAD_PRE_SPLIT:.*]]
+
+;; Cast in "right.left" should not have a debug location, as we are not
+;; guaranteed to reach the load's original position.
+; CHECK: [[RIGHT_LEFT]]:
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr [[P]], i8 0, i64 8, i1 false)
+; CHECK-NEXT: [[TMP1:%.*]] = inttoptr i64 0 to ptr
+; CHECK-NEXT: br i1 {{.*}}, label %[[END]], label %[[EXIT:.*]]
+
+;; Load in "right.right" should have the load's debug location.
+; CHECK: [[ENDTHREAD_PRE_SPLIT]]:
+; CHECK-NEXT: [[DOTPR:%.*]] = load ptr, ptr [[P]], align 8, !dbg [[LOAD_LOC]]
+; CHECK-NEXT: br label %[[END]], !dbg [[LOAD_LOC]]
+
+;; Finally, the PHI node should also have the load's debug location.
+; CHECK: [[END]]:
+; CHECK-NEXT: [[TMP2:%.*]] = phi ptr [ [[DOTPR]], %[[ENDTHREAD_PRE_SPLIT]] ], [ [[TMP1]], %[[RIGHT_LEFT]] ], [ [[TMP0]], %[[LEFT]] ], !dbg [[LOAD_LOC]]
+
+; CHECK: [[LOAD_LOC]] = !DILocation(line: 1, column: 1,
+
+define void @foo(i1 %b, i1 %c, i1 %d) !dbg !5 {
+entry:
+ %p = alloca i32, align 8
+ br i1 %b, label %left, label %right
+
+left:
+ call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 8, i1 false)
+ br label %end
+
+right:
+ br i1 %c, label %right.left, label %right.right
+
+right.left:
+ call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 8, i1 false)
+ br i1 %d, label %end, label %exit
+
+right.right:
+ br label %end
+
+end:
+ %0 = load ptr, ptr %p, align 8, !dbg !8
+ %isnull = icmp eq ptr %0, null
+ br i1 %isnull, label %exit, label %notnull
+
+notnull:
+ br label %exit
+
+exit:
+ ret void
+}
+
+; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: write)
+declare void @llvm.memset.p0.i64(ptr writeonly captures(none), i8, i64, i1 immarg) #0
+
+attributes #0 = { nocallback nofree nounwind willreturn memory(argmem: write) }
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "simplify-partially-redundant-load-debugloc.ll", directory: "/")
+!2 = !{i32 13}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: !0, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5)
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