[DeadArgumentElimination] Preserve llvm.dbg.values's first argument

When removing return value Dead Argument Elimination pass clobbers first
llvm.dbg.value’s argument for live arguments of that function by replacing
it with nullptr. In the next pass it will be deleted, so debug location
about those arguments are lost. This change fixes it.

Patch by Djordje Todorovic.

Differential Revision: https://reviews.llvm.org/D42541

llvm-svn: 323784

2 files changed, 151 insertions, 8 deletions

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index a148ab65fc8..4f49312dfc4 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -329,12 +329,20 @@ bool ReplaceableMetadataImpl::isReplaceable(const Metadata &MD) {
   return dyn_cast<ValueAsMetadata>(&MD);
 }
 
-static Function *getLocalFunction(Value *V) {
+static DISubprogram *getLocalFunctionMetadata(Value *V) {
   assert(V && "Expected value");
-  if (auto *A = dyn_cast<Argument>(V))
-    return A->getParent();
-  if (BasicBlock *BB = cast<Instruction>(V)->getParent())
-    return BB->getParent();
+  if (auto *A = dyn_cast<Argument>(V)) {
+    if (auto *Fn = A->getParent())
+      return Fn->getSubprogram();
+    return nullptr;
+  }
+
+  if (BasicBlock *BB = cast<Instruction>(V)->getParent()) {
+    if (auto *Fn = BB->getParent())
+      return Fn->getSubprogram();
+    return nullptr;
+  }
+
   return nullptr;
 }
 
@@ -410,9 +418,9 @@ void ValueAsMetadata::handleRAUW(Value *From, Value *To) {
       delete MD;
       return;
     }
-    if (getLocalFunction(From) && getLocalFunction(To) &&
-        getLocalFunction(From) != getLocalFunction(To)) {
-      // Function changed.
+    if (getLocalFunctionMetadata(From) && getLocalFunctionMetadata(To) &&
+        getLocalFunctionMetadata(From) != getLocalFunctionMetadata(To)) {
+      // DISubprogram changed.
       MD->replaceAllUsesWith(nullptr);
       delete MD;
       return;
diff --git a/llvm/test/Transforms/DeadArgElim/dbginfo-preserve-dbgloc.ll b/llvm/test/Transforms/DeadArgElim/dbginfo-preserve-dbgloc.ll
new file mode 100644
index 00000000000..e83202c5d54
--- /dev/null
+++ b/llvm/test/Transforms/DeadArgElim/dbginfo-preserve-dbgloc.ll
@@ -0,0 +1,135 @@
+; RUN: opt -deadargelim -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+%struct.Channel = type { i32, i32 }
+
+; Function Attrs: nounwind uwtable
+define void @f2(i32 %m, i32 %n) #0 !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %m, metadata !12, metadata !DIExpression()), !dbg !21
+  call void @llvm.dbg.value(metadata i32 %n, metadata !13, metadata !DIExpression()), !dbg !22
+  call void @llvm.dbg.value(metadata %struct.Channel* null, metadata !14, metadata !DIExpression()), !dbg !23
+  %call = call %struct.Channel* (...) @foo(), !dbg !24
+  call void @llvm.dbg.value(metadata %struct.Channel* %call, metadata !14, metadata !DIExpression()), !dbg !23
+  %cmp = icmp sgt i32 %m, 3, !dbg !25
+  br i1 %cmp, label %if.then, label %if.end, !dbg !27
+
+if.then:                                          ; preds = %entry
+  %call1 = call zeroext i1 @f1(i1 zeroext true, %struct.Channel* %call), !dbg !28
+  br label %if.end, !dbg !28
+
+if.end:                                           ; preds = %if.then, %entry
+  %cmp2 = icmp sgt i32 %n, %m, !dbg !29
+  br i1 %cmp2, label %if.then3, label %if.end5, !dbg !31
+
+if.then3:                                         ; preds = %if.end
+  %call4 = call zeroext i1 @f1(i1 zeroext false, %struct.Channel* %call), !dbg !32
+  br label %if.end5, !dbg !32
+
+if.end5:                                          ; preds = %if.then3, %if.end
+  ret void, !dbg !33
+}
+
+declare %struct.Channel* @foo(...) local_unnamed_addr #1
+
+; Function Attrs: noinline nounwind uwtable
+define internal zeroext i1 @f1(i1 zeroext %is_y, %struct.Channel* %str) #4 !dbg !34 {
+entry:
+  %frombool = zext i1 %is_y to i8
+; CHECK: call void @llvm.dbg.value(metadata i1 %is_y, metadata !39, metadata !DIExpression()), !dbg !42
+  call void @llvm.dbg.value(metadata i1 %is_y, metadata !39, metadata !DIExpression()), !dbg !42
+; CHECK: call void @llvm.dbg.value(metadata %struct.Channel* %str, metadata !40, metadata !DIExpression()), !dbg !43
+  call void @llvm.dbg.value(metadata %struct.Channel* %str, metadata !40, metadata !DIExpression()), !dbg !43
+  call void @llvm.dbg.value(metadata %struct.Channel* null, metadata !41, metadata !DIExpression()), !dbg !44
+  %tobool = icmp ne %struct.Channel* %str, null, !dbg !45
+  br i1 %tobool, label %if.end, label %if.then, !dbg !47
+
+if.then:                                          ; preds = %entry
+  call void (...) @baa(), !dbg !48
+  br label %cleanup, !dbg !50
+
+if.end:                                           ; preds = %entry
+  %call = call %struct.Channel* (...) @foo(), !dbg !51
+  call void @llvm.dbg.value(metadata %struct.Channel* %call, metadata !41, metadata !DIExpression()), !dbg !44
+  %tobool1 = trunc i8 %frombool to i1, !dbg !52
+  br i1 %tobool1, label %if.then2, label %if.end3, !dbg !56
+
+if.then2:                                         ; preds = %if.end
+  call void (...) @baa(), !dbg !57
+  br label %cleanup, !dbg !56
+
+if.end3:                                          ; preds = %if.end
+  br label %cleanup, !dbg !56
+
+cleanup:                                          ; preds = %if.end3, %if.then2, %if.then
+  %retval.0 = phi i1 [ false, %if.then2 ], [ true, %if.end3 ], [ false, %if.then ]
+  ret i1 %retval.0, !dbg !56
+}
+
+declare void @baa(...) local_unnamed_addr #1
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #3
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 7.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/dir")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0"}
+!7 = distinct !DISubprogram(name: "f2", scope: !1, file: !1, line: 31, type: !8, isLocal: false, isDefinition: true, scopeLine: 32, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12, !13, !14}
+!12 = !DILocalVariable(name: "m", arg: 1, scope: !7, file: !1, line: 31, type: !10)
+!13 = !DILocalVariable(name: "n", arg: 2, scope: !7, file: !1, line: 31, type: !10)
+!14 = !DILocalVariable(name: "str3", scope: !7, file: !1, line: 33, type: !15)
+!15 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
+!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "channel", file: !1, line: 6, baseType: !17)
+!17 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Channel", file: !1, line: 3, size: 64, elements: !18)
+!18 = !{!19, !20}
+!19 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !17, file: !1, line: 4, baseType: !10, size: 32)
+!20 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !17, file: !1, line: 5, baseType: !10, size: 32, offset: 32)
+!21 = !DILocation(line: 31, column: 13, scope: !7)
+!22 = !DILocation(line: 31, column: 20, scope: !7)
+!23 = !DILocation(line: 33, column: 11, scope: !7)
+!24 = !DILocation(line: 34, column: 9, scope: !7)
+!25 = !DILocation(line: 36, column: 8, scope: !26)
+!26 = distinct !DILexicalBlock(scope: !7, file: !1, line: 36, column: 6)
+!27 = !DILocation(line: 36, column: 6, scope: !7)
+!28 = !DILocation(line: 37, column: 3, scope: !26)
+!29 = !DILocation(line: 39, column: 8, scope: !30)
+!30 = distinct !DILexicalBlock(scope: !7, file: !1, line: 39, column: 6)
+!31 = !DILocation(line: 39, column: 6, scope: !7)
+!32 = !DILocation(line: 40, column: 3, scope: !30)
+!33 = !DILocation(line: 41, column: 1, scope: !7)
+!34 = distinct !DISubprogram(name: "f1", scope: !1, file: !1, line: 12, type: !35, isLocal: true, isDefinition: true, scopeLine: 13, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !38)
+!35 = !DISubroutineType(types: !36)
+!36 = !{!37, !37, !15}
+!37 = !DIBasicType(name: "_Bool", size: 8, encoding: DW_ATE_boolean)
+!38 = !{!39, !40, !41}
+!39 = !DILocalVariable(name: "is_y", arg: 1, scope: !34, file: !1, line: 12, type: !37)
+!40 = !DILocalVariable(name: "str", arg: 2, scope: !34, file: !1, line: 12, type: !15)
+!41 = !DILocalVariable(name: "str2", scope: !34, file: !1, line: 14, type: !15)
+!42 = !DILocation(line: 12, column: 21, scope: !34)
+!43 = !DILocation(line: 12, column: 36, scope: !34)
+!44 = !DILocation(line: 14, column: 11, scope: !34)
+!45 = !DILocation(line: 16, column: 7, scope: !46)
+!46 = distinct !DILexicalBlock(scope: !34, file: !1, line: 16, column: 6)
+!47 = !DILocation(line: 16, column: 6, scope: !34)
+!48 = !DILocation(line: 17, column: 3, scope: !49)
+!49 = distinct !DILexicalBlock(scope: !46, file: !1, line: 16, column: 11)
+!50 = !DILocation(line: 18, column: 3, scope: !49)
+!51 = !DILocation(line: 21, column: 9, scope: !34)
+!52 = !DILocation(line: 23, column: 6, scope: !34)
+!53 = !DILocation(line: 24, column: 3, scope: !54)
+!54 = distinct !DILexicalBlock(scope: !55, file: !1, line: 23, column: 11)
+!55 = distinct !DILexicalBlock(scope: !34, file: !1, line: 23, column: 6)
+!56 = !DILocation(line: 25, column: 3, scope: !54)
+!57 = !DILocation(line: 28, column: 2, scope: !34)