Fix a nondeterminism in the debug info for VLA size expressions.

The artificial variable describing the array size is supposed to be
called "__vla_expr", but this was implemented by retrieving the name
of the associated alloca, which isn't a reliable source for the name,
since nonassert compilers may drop names from LLVM IR.

rdar://problem/45924808

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@346542 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGDecl.cpp

@@ -1066,6 +1066,7 @@ void CodeGenFunction::EmitAndRegisterVariableArrayDimensions(
   // For each dimension stores its QualType and corresponding
   // size-expression Value.
   SmallVector<CodeGenFunction::VlaSizePair, 4> Dimensions;
+  SmallVector<IdentifierInfo *, 4> VLAExprNames;
 
   // Break down the array into individual dimensions.
   QualType Type1D = D.getType();
@@ -1074,8 +1075,14 @@ void CodeGenFunction::EmitAndRegisterVariableArrayDimensions(
     if (auto *C = dyn_cast<llvm::ConstantInt>(VlaSize.NumElts))
       Dimensions.emplace_back(C, Type1D.getUnqualifiedType());
     else {
-      auto SizeExprAddr = CreateDefaultAlignTempAlloca(
-          VlaSize.NumElts->getType(), "__vla_expr");
+      // Generate a locally unique name for the size expression.
+      Twine Name = Twine("__vla_expr") + Twine(VLAExprCounter++);
+      SmallString<12> Buffer;
+      StringRef NameRef = Name.toStringRef(Buffer);
+      auto &Ident = getContext().Idents.getOwn(NameRef);
+      VLAExprNames.push_back(&Ident);
+      auto SizeExprAddr =
+          CreateDefaultAlignTempAlloca(VlaSize.NumElts->getType(), NameRef);
       Builder.CreateStore(VlaSize.NumElts, SizeExprAddr);
       Dimensions.emplace_back(SizeExprAddr.getPointer(),
                               Type1D.getUnqualifiedType());
@@ -1089,20 +1096,20 @@ void CodeGenFunction::EmitAndRegisterVariableArrayDimensions(
   // Register each dimension's size-expression with a DILocalVariable,
   // so that it can be used by CGDebugInfo when instantiating a DISubrange
   // to describe this array.
+  unsigned NameIdx = 0;
   for (auto &VlaSize : Dimensions) {
     llvm::Metadata *MD;
     if (auto *C = dyn_cast<llvm::ConstantInt>(VlaSize.NumElts))
       MD = llvm::ConstantAsMetadata::get(C);
     else {
       // Create an artificial VarDecl to generate debug info for.
-      IdentifierInfo &NameIdent = getContext().Idents.getOwn(
-          cast<llvm::AllocaInst>(VlaSize.NumElts)->getName());
+      IdentifierInfo *NameIdent = VLAExprNames[NameIdx++];
       auto VlaExprTy = VlaSize.NumElts->getType()->getPointerElementType();
       auto QT = getContext().getIntTypeForBitwidth(
           VlaExprTy->getScalarSizeInBits(), false);
       auto *ArtificialDecl = VarDecl::Create(
           getContext(), const_cast<DeclContext *>(D.getDeclContext()),
-          D.getLocation(), D.getLocation(), &NameIdent, QT,
+          D.getLocation(), D.getLocation(), NameIdent, QT,
           getContext().CreateTypeSourceInfo(QT), SC_Auto);
       ArtificialDecl->setImplicit();
 

lib/CodeGen/CodeGenFunction.h

@@ -1197,6 +1197,8 @@ public:
 
 private:
   CGDebugInfo *DebugInfo;
+  /// Used to create unique names for artificial VLA size debug info variables.
+  unsigned VLAExprCounter = 0;
   bool DisableDebugInfo = false;
 
   /// DidCallStackSave - Whether llvm.stacksave has been called. Used to avoid

test/CodeGen/debug-info-vla.c

@@ -2,9 +2,9 @@
 
 void testVLAwithSize(int s)
 {
-// CHECK-DAG: dbg.declare({{.*}} %__vla_expr, metadata ![[VLAEXPR:[0-9]+]]
+// CHECK-DAG: dbg.declare({{.*}} %__vla_expr0, metadata ![[VLAEXPR:[0-9]+]]
 // CHECK-DAG: dbg.declare({{.*}} %vla, metadata ![[VAR:[0-9]+]]
-// CHECK-DAG: ![[VLAEXPR]] = !DILocalVariable(name: "__vla_expr", {{.*}} flags: DIFlagArtificial
+// CHECK-DAG: ![[VLAEXPR]] = !DILocalVariable(name: "__vla_expr0", {{.*}} flags: DIFlagArtificial
 // CHECK-DAG: ![[VAR]] = !DILocalVariable(name: "vla",{{.*}} line: [[@LINE+2]]
 // CHECK-DAG: !DISubrange(count: ![[VLAEXPR]])
   int vla[s];

test/CodeGenCXX/debug-info-vla.cpp

@@ -13,7 +13,7 @@ int (*fp)(int[][*]) = nullptr;
 // CHECK: [[ELEM_TYPE]] = !{[[NOCOUNT:.*]]}
 // CHECK: [[NOCOUNT]] = !DISubrange(count: -1)
 //
-// CHECK: [[VAR:![0-9]+]] = !DILocalVariable(name: "__vla_expr", {{.*}}flags: DIFlagArtificial
+// CHECK: [[VAR:![0-9]+]] = !DILocalVariable(name: "__vla_expr0", {{.*}}flags: DIFlagArtificial
 // CHECK: !DICompositeType(tag: DW_TAG_array_type,
 // CHECK-NOT:                               size:
 // CHECK-SAME:                              elements: [[ELEM_TYPE:![0-9]+]]