[SystemZ] Bugfix in expandRxSBG()
Csmith discovered a program that caused wrong code generation with -O0:
When handling a SIGN_EXTEND in expandRxSBG(), RxSBG.BitSize may be less than
the Input width (if a truncate was previously traversed), so maskMatters()
should be called with a masked based on the width of the sign extend result
instead.
Review: Ulrich Weigand
llvm-svn: 319892
diff --git a/llvm/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp b/llvm/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp
index 3073d2f..ce6f3d3 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp
@@ -838,9 +838,16 @@
case ISD::SIGN_EXTEND: {
// Check that the extension bits are don't-care (i.e. are masked out
// by the final mask).
+ unsigned BitSize = N.getValueSizeInBits();
unsigned InnerBitSize = N.getOperand(0).getValueSizeInBits();
- if (maskMatters(RxSBG, allOnes(RxSBG.BitSize) - allOnes(InnerBitSize)))
- return false;
+ if (maskMatters(RxSBG, allOnes(BitSize) - allOnes(InnerBitSize))) {
+ // In the case where only the sign bit is active, increase Rotate with
+ // the extension width.
+ if (RxSBG.Mask == 1 && RxSBG.Rotate == 1)
+ RxSBG.Rotate += (BitSize - InnerBitSize);
+ else
+ return false;
+ }
RxSBG.Input = N.getOperand(0);
return true;