[PATCH] D100165: [GVNHoist] fix a bug where GVNHoist preserves the debug location when it should be dropped

[Yuanbo Li via Phabricator via llvm-commits]

yuanboli233 updated this revision to Diff 336929.
yuanboli233 added a comment.

I thought the previous CHECK will discard store instructions with drop location. Thanks for pointing it out @aprantl, I have added the comment and change the CHECK. I have tested that the test case can now distinguish the versions before and after the proposed patch.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100165/new/

https://reviews.llvm.org/D100165

Files:
  llvm/lib/Transforms/Scalar/GVNHoist.cpp
  llvm/test/Transforms/GVNHoist/hoist_debugloc.ll


Index: llvm/test/Transforms/GVNHoist/hoist_debugloc.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/GVNHoist/hoist_debugloc.ll
@@ -0,0 +1,59 @@
+; RUN: opt -gvn-hoist %s -S 2>&1 | FileCheck %s
+; COM: check whether the hoisted store instruction drops the debug location.
+; CHECK: store i32 1, i32* @{{[a-zA-Z_][a-zA-Z0-9_]*}}, align 4{{$}}
+source_filename = "abc.ll"
+
+ at G = external global i32, align 4
+
+define void @foo(i32 %c1) !dbg !6 {
+entry:
+  call void @llvm.dbg.value(metadata i32 0, metadata !9, metadata !DIExpression()), !dbg !11
+  switch i32 %c1, label %exit1 [
+    i32 0, label %sw0
+    i32 1, label %sw1
+  ], !dbg !11
+
+sw0:                                              ; preds = %entry
+  store i32 1, i32* @G, align 4, !dbg !12
+  br label %exit, !dbg !13
+
+sw1:                                              ; preds = %entry
+  store i32 1, i32* @G, align 4, !dbg !14
+  br label %exit, !dbg !15
+
+exit1:                                            ; preds = %entry
+  store i32 1, i32* @G, align 4, !dbg !16
+  ret void, !dbg !17
+
+exit:                                             ; preds = %sw1, %sw0
+  ret void, !dbg !18
+}
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+
+attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "abc.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 8}
+!4 = !{i32 1}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+!10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+!11 = !DILocation(line: 1, column: 1, scope: !6)
+!12 = !DILocation(line: 2, column: 1, scope: !6)
+!13 = !DILocation(line: 3, column: 1, scope: !6)
+!14 = !DILocation(line: 4, column: 1, scope: !6)
+!15 = !DILocation(line: 5, column: 1, scope: !6)
+!16 = !DILocation(line: 6, column: 1, scope: !6)
+!17 = !DILocation(line: 7, column: 1, scope: !6)
+!18 = !DILocation(line: 8, column: 1, scope: !6)
Index: llvm/lib/Transforms/Scalar/GVNHoist.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVNHoist.cpp
+++ llvm/lib/Transforms/Scalar/GVNHoist.cpp
@@ -1140,6 +1140,11 @@
       // Move the instruction at the end of HoistPt.
       Instruction *Last = DestBB->getTerminator();
       MD->removeInstruction(Repl);
+      // if there are multiple instructions to hoist, we should conservatively
+      // drop the debug location: according to the LLVM debug information update
+      // guide, if multiple identical instructions are hoisted into a
+      // predecessor block, the debug information should not be preserved.
+      Repl->dropLocation();
       Repl->moveBefore(Last);
 
       DFSNumber[Repl] = DFSNumber[Last]++;


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