AMDGPU: Allow negative MUBUF vaddr for gfx9
GFX9 does not enable bounds checking for the resource descriptors
used for private access, so it should be OK to use vaddr with
a potentially negative value.
llvm-svn: 319393
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
index 836c706..79d8de9 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
@@ -1158,14 +1158,25 @@
SDValue N0 = Addr.getOperand(0);
SDValue N1 = Addr.getOperand(1);
- // Offsets in vaddr must be positive.
+ // Offsets in vaddr must be positive if range checking is enabled.
//
- // The total computation of vaddr + soffset + offset must not overflow.
- // If vaddr is negative, even if offset is 0 the sgpr offset add will end up
+ // The total computation of vaddr + soffset + offset must not overflow. If
+ // vaddr is negative, even if offset is 0 the sgpr offset add will end up
// overflowing.
+ //
+ // Prior to gfx9, MUBUF instructions with the vaddr offset enabled would
+ // always perform a range check. If a negative vaddr base index was used,
+ // this would fail the range check. The overall address computation would
+ // compute a valid address, but this doesn't happen due to the range
+ // check. For out-of-bounds MUBUF loads, a 0 is returned.
+ //
+ // Therefore it should be safe to fold any VGPR offset on gfx9 into the
+ // MUBUF vaddr, but not on older subtargets which can only do this if the
+ // sign bit is known 0.
ConstantSDNode *C1 = cast<ConstantSDNode>(N1);
if (SIInstrInfo::isLegalMUBUFImmOffset(C1->getZExtValue()) &&
- CurDAG->SignBitIsZero(N0)) {
+ (!Subtarget->privateMemoryResourceIsRangeChecked() ||
+ CurDAG->SignBitIsZero(N0))) {
std::tie(VAddr, SOffset) = foldFrameIndex(N0);
ImmOffset = CurDAG->getTargetConstant(C1->getZExtValue(), DL, MVT::i16);
return true;