[deadargelim] Update dbg.value of 'unused' parameters

DeadArgElim pass marks unused function arguments as ‘undef’ without updating
existing dbg.values referring to it. As a consequence the debug info
metadata in the final executable was wrong.

Patch by Djordje Todorovic.

Differential Revision: https://reviews.llvm.org/D51968

llvm-svn: 342871

llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp

@@ -289,16 +289,21 @@ bool DeadArgumentEliminationPass::RemoveDeadArgumentsFromCallers(Function &Fn) {
     return false;
 
   SmallVector<unsigned, 8> UnusedArgs;
+  bool Changed = false;
+
   for (Argument &Arg : Fn.args()) {
-    if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() && !Arg.hasByValOrInAllocaAttr())
+    if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() && !Arg.hasByValOrInAllocaAttr()) {
+      if (Arg.isUsedByMetadata()) {
+        Arg.replaceAllUsesWith(UndefValue::get(Arg.getType()));
+        Changed = true;
+      }
       UnusedArgs.push_back(Arg.getArgNo());
+    }
   }
 
   if (UnusedArgs.empty())
     return false;
 
-  bool Changed = false;
-
   for (Use &U : Fn.uses()) {
     CallSite CS(U.getUser());
     if (!CS || !CS.isCallee(&U))

llvm/test/Transforms/DeadArgElim/dbginfo-update-dbgval.ll

@@ -0,0 +1,86 @@
+; RUN: opt -deadargelim -S < %s | FileCheck %s
+;test.c
+;int s;
+;
+;void f2(int k) __attribute__((noinline)) {
+; s++;
+; k = s;
+;}
+;
+;void f() __attribute__((noinline)) {
+; f2(4);
+;}
+;
+;int main()
+;{
+; f();
+; return 0;
+;}
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+@s = common dso_local local_unnamed_addr global i32 0, align 4, !dbg !0
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local void @f2(i32 %k) local_unnamed_addr !dbg !11 {
+entry:
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata !15, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 %k, metadata !15, metadata !DIExpression()), !dbg !16
+  %0 = load i32, i32* @s, align 4, !dbg !17
+  %inc = add nsw i32 %0, 1, !dbg !17
+  store i32 %inc, i32* @s, align 4, !dbg !17
+  call void @llvm.dbg.value(metadata i32* @s, metadata !15, metadata !DIExpression(DW_OP_deref)), !dbg !16
+  ret void, !dbg !18
+}
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local void @f() local_unnamed_addr !dbg !19 {
+entry:
+; CHECK: tail call void @f2(i32 undef), !dbg !22
+  tail call void @f2(i32 4), !dbg !22
+  ret void, !dbg !23
+}
+
+; Function Attrs: nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr !dbg !24 {
+entry:
+  tail call void @f(), !dbg !27
+  ret i32 0, !dbg !28
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "s", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 8.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "test.c", directory: "/dir")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 7.0.0"}
+!11 = distinct !DISubprogram(name: "f2", scope: !3, file: !3, line: 3, type: !12, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !2, retainedNodes: !14)
+!12 = !DISubroutineType(types: !13)
+!13 = !{null, !6}
+!14 = !{!15}
+!15 = !DILocalVariable(name: "k", arg: 1, scope: !11, file: !3, line: 3, type: !6)
+!16 = !DILocation(line: 3, column: 13, scope: !11)
+!17 = !DILocation(line: 4, column: 3, scope: !11)
+!18 = !DILocation(line: 6, column: 1, scope: !11)
+!19 = distinct !DISubprogram(name: "f", scope: !3, file: !3, line: 8, type: !20, isLocal: false, isDefinition: true, scopeLine: 8, isOptimized: true, unit: !2, retainedNodes: !4)
+!20 = !DISubroutineType(types: !21)
+!21 = !{null}
+!22 = !DILocation(line: 9, column: 2, scope: !19)
+!23 = !DILocation(line: 10, column: 1, scope: !19)
+!24 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 12, type: !25, isLocal: false, isDefinition: true, scopeLine: 12, isOptimized: true, unit: !2, retainedNodes: !4)
+!25 = !DISubroutineType(types: !26)
+!26 = !{!6}
+!27 = !DILocation(line: 13, column: 2, scope: !24)
+!28 = !DILocation(line: 14, column: 2, scope: !24)