[globalopt] Don't emit DWARF fragments for members

of a struct that cover the whole struct

This can happen when the rest of the
members of are zero length. Following
the same pattern applied to the SROA
pass in:
d7f6f1636d53c3e2faf55cdf20fbb44a1a149df1

Fixes: https://bugs.llvm.org/show_bug.cgi?id=45335

Differential Revision: https://reviews.llvm.org/D78720

(cherry picked from commit 3929429347d398773577b79f7fdb780d4f7ed887)

1 files changed, 10 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 0fd966457ec..b75e853553c 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -450,14 +450,19 @@ static bool CanDoGlobalSRA(GlobalVariable *GV) {
 /// Copy over the debug info for a variable to its SRA replacements.
 static void transferSRADebugInfo(GlobalVariable *GV, GlobalVariable *NGV,
                                  uint64_t FragmentOffsetInBits,
-                                 uint64_t FragmentSizeInBits,
-                                 unsigned NumElements) {
+                                 uint64_t FragmentSizeInBits) {
   SmallVector<DIGlobalVariableExpression *, 1> GVs;
   GV->getDebugInfo(GVs);
   for (auto *GVE : GVs) {
     DIVariable *Var = GVE->getVariable();
+    Optional<uint64_t> VarSize = Var->getSizeInBits();
+
     DIExpression *Expr = GVE->getExpression();
-    if (NumElements > 1) {
+    // If the FragmentSize is smaller than the variable,
+    // emit a fragment expression.
+    // If the variable size is unknown a fragment must be
+    // emitted to be safe.
+    if (!VarSize || FragmentSizeInBits < *VarSize) {
       if (auto E = DIExpression::createFragmentExpression(
               Expr, FragmentOffsetInBits, FragmentSizeInBits))
         Expr = *E;
@@ -539,8 +544,7 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
       // Copy over the debug info for the variable.
       uint64_t Size = DL.getTypeAllocSizeInBits(NGV->getValueType());
       uint64_t FragmentOffsetInBits = Layout.getElementOffsetInBits(ElementIdx);
-      transferSRADebugInfo(GV, NGV, FragmentOffsetInBits, Size,
-                           STy->getNumElements());
+      transferSRADebugInfo(GV, NGV, FragmentOffsetInBits, Size);
     } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
       uint64_t EltSize = DL.getTypeAllocSize(ElTy);
       Align EltAlign(DL.getABITypeAlignment(ElTy));
@@ -553,7 +557,7 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
       if (NewAlign > EltAlign)
         NGV->setAlignment(NewAlign);
       transferSRADebugInfo(GV, NGV, FragmentSizeInBits * ElementIdx,
-                           FragmentSizeInBits, STy->getNumElements());
+                           FragmentSizeInBits);
     }
   }