Debug info: When updating debug info during SROA, do not emit debug info

for any padding introduced by SROA. In particular, do not emit debug info
for an alloca that represents only the padding introduced by a previous
iteration.

Fixes PR22495.

llvm-svn: 228632

1 files changed, 18 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index eaf73ee5e68..f69c750f3f9 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -4153,8 +4153,13 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
   for (auto &P : AS.partitions()) {
     if (AllocaInst *NewAI = rewritePartition(AI, AS, P)) {
       Changed = true;
-      if (NewAI != &AI)
-        Pieces.push_back(Piece(NewAI, P.beginOffset(), P.size()));
+      if (NewAI != &AI) {
+        uint64_t SizeOfByte = 8;
+        uint64_t AllocaSize = DL->getTypeSizeInBits(NewAI->getAllocatedType());
+        // Don't include any padding.
+        uint64_t Size = std::min(AllocaSize, P.size() * SizeOfByte);
+        Pieces.push_back(Piece(NewAI, P.beginOffset() * SizeOfByte, Size));
+      }
     }
     ++NumPartitions;
   }
@@ -4178,12 +4183,17 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
       if (IsSplit || Expr.isBitPiece()) {
         // If this alloca is already a scalar replacement of a larger aggregate,
         // Piece.Offset describes the offset inside the scalar.
-        unsigned Offset = Expr.isBitPiece() ? Expr.getBitPieceOffset() : 0;
-        assert((Offset == 0 ||
-                Offset+Piece.Offset+Piece.Size*8 <=
-                Expr.getBitPieceOffset()+Expr.getBitPieceSize()) &&
-                "inner piece is not inside original alloca");
-        PieceExpr = DIB.createBitPieceExpression(Offset+Piece.Offset*8, Piece.Size*8);
+        uint64_t Offset = Expr.isBitPiece() ? Expr.getBitPieceOffset() : 0;
+        uint64_t Start = Offset + Piece.Offset;
+        uint64_t Size = Piece.Size;
+        if (Expr.isBitPiece()) {
+          uint64_t AbsEnd = Expr.getBitPieceOffset() + Expr.getBitPieceSize();
+          if (Start >= AbsEnd)
+            // No need to describe a SROAed padding.
+            continue;
+          Size = std::min(Size, AbsEnd - Start);
+        }
+        PieceExpr = DIB.createBitPieceExpression(Start, Size);
       }
 
       // Remove any existing dbg.declare intrinsic describing the same alloca.