[PATCH] D80819: [DebugInfo][DAG] Don't reuse debug location on COPY if width changes.

[Tobias Bosch via Phabricator via llvm-commits]

tbosch created this revision.
Herald added subscribers: llvm-commits, hiraditya, aprantl.
Herald added a project: LLVM.
tbosch added a reviewer: vsk.
tbosch added a subscriber: dblaikie.

This caused incorrect debug information for parameters:
Previously, after a COPY of a parameter that changes the width,
we would emit a DBG_VALUE that continues to be associated to that
parameter, even though it now used a different width.
This made the LiveDebugValues pass assume the parameter value
got clobbered and it stopped tracking the parameter entry
value, leading to incorrect debug information.

Fixes https://bugs.llvm.org/show_bug.cgi?id=39715


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80819

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
  llvm/test/DebugInfo/X86/dbg-value-funcarg3.ll


Index: llvm/test/DebugInfo/X86/dbg-value-funcarg3.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/dbg-value-funcarg3.ll
@@ -0,0 +1,58 @@
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu -start-after=codegenprepare -stop-before=finalize-isel -o - %s | FileCheck %s
+
+; Input to this test looked like this and was compiled using: clang -g -O1 -mllvm -stop-after=codegenprepare -S
+;
+;    int fn1(long t1) {
+;      return t;
+;    }
+;
+
+; Catch metadata references for involved variables.
+;
+; CHECK-DAG: ![[T1:.*]] = !DILocalVariable(name: "t1"
+
+
+define dso_local i32 @fn1(i64 %t1) local_unnamed_addr #0 !dbg !7 {
+; We expect that the same width COPY reuses the debug location,
+; but the width narrowing COPY does not.
+; 
+; CHECK-LABEL: name:            fn1
+; CHECK: DBG_VALUE $rdi, $noreg, ![[T1]], !DIExpression(),
+; CHECK-NEXT: %0:gr64 = COPY $rdi
+; CHECK-NEXT: DBG_VALUE %0, $noreg, ![[T1]], !DIExpression(),
+; CHECK-NEXT: %1:gr32 = COPY %0.sub_32bit
+; CHECK-NEXT: COPY
+; CHECK-NEXT: RET
+entry:
+  call void @llvm.dbg.value(metadata i64 %t1, metadata !13, metadata !DIExpression()), !dbg !14
+  %0 = trunc i64 %t1 to i32, !dbg !15
+  ret i32 %0, !dbg !16
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { norecurse nounwind readnone uwtable }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 11.0.0 (git at github.com:tbosch/llvm-project.git 0b11aed869bf09ba60
+d7ed17334cf0b76e6a5922)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cc", directory: "")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0 (git at github.com:tbosch/llvm-project.git 0b11aed869bf09ba60d7ed17334cf0b76e6a5922)"}
+!7 = distinct !DISubprogram(name: "fn1", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !11}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!12 = !{!13}
+!13 = !DILocalVariable(name: "t1", arg: 1, scope: !7, file: !1, line: 1, type: !11)
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !DILocation(line: 2, column: 10, scope: !7)
+!16 = !DILocation(line: 2, column: 3, scope: !7)
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -617,8 +617,11 @@
            E = RegInfo->use_instr_end(); UI != E; ) {
         MachineInstr *UseMI = &*(UI++);
         if (UseMI->isDebugValue()) continue;
-        if (UseMI->isCopy() && !CopyUseMI && UseMI->getParent() == EntryMBB) {
-          CopyUseMI = UseMI; continue;
+        if (UseMI->isCopy() && !CopyUseMI && UseMI->getParent() == EntryMBB &&
+            TRI.getRegSizeInBits(LDI->second, MRI) ==
+                TRI.getRegSizeInBits(UseMI->getOperand(0).getReg(), MRI)) {
+          CopyUseMI = UseMI;
+          continue;
         }
         // Otherwise this is another use or second copy use.
         CopyUseMI = nullptr; break;


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