[GlobalOpt] Emit fragments using field offsets from struct layout

Summary:
When creating the debug fragments for a SRA'd struct, use the fields'
offsets, taken from the struct layout, as the offsets for the resulting
fragments. This fixes an issue where GlobalOpt would emit fragments with
incorrect offsets for padded fields.

This should solve PR36016.

Patch by David Stenberg.

Reviewers: aprantl

Reviewed By: aprantl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42489

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@323411 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/GlobalOpt.cpp

@@ -483,7 +483,6 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
     StartAlignment = DL.getABITypeAlignment(GV->getType());
 
   if (StructType *STy = dyn_cast<StructType>(Ty)) {
-    uint64_t FragmentOffset = 0;
     unsigned NumElements = STy->getNumElements();
     NewGlobals.reserve(NumElements);
     const StructLayout &Layout = *DL.getStructLayout(STy);
@@ -509,10 +508,9 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
         NGV->setAlignment(NewAlign);
 
       // Copy over the debug info for the variable.
-      FragmentOffset = alignTo(FragmentOffset, NewAlign);
       uint64_t Size = DL.getTypeSizeInBits(NGV->getValueType());
-      transferSRADebugInfo(GV, NGV, FragmentOffset, Size, NumElements);
-      FragmentOffset += Size;
+      uint64_t FragmentOffsetInBits = Layout.getElementOffsetInBits(i);
+      transferSRADebugInfo(GV, NGV, FragmentOffsetInBits, Size, NumElements);
     }
   } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
     unsigned NumElements = STy->getNumElements();

test/DebugInfo/Generic/global-sra-struct.ll

@@ -24,7 +24,7 @@ target triple = "x86_64-apple-macosx10.12.0"
 
 ; CHECK: ![[EL0]] = !DIGlobalVariableExpression(var: ![[VAR:.*]], expr: !DIExpression(DW_OP_LLVM_fragment, 0, 32))
 ; CHECK: ![[VAR]] = distinct !DIGlobalVariable(name: "static_struct"
-; CHECK: ![[EL1]] = !DIGlobalVariableExpression(var: ![[VAR]], expr: !DIExpression(DW_OP_LLVM_fragment, 32, 64))
+; CHECK: ![[EL1]] = !DIGlobalVariableExpression(var: ![[VAR]], expr: !DIExpression(DW_OP_LLVM_fragment, 64, 64))
 
 @static_struct = internal global %struct.mystruct zeroinitializer, align 8, !dbg !0