[AMDGPU] UBSan bug fix for r345710

UBSan detected an error in our ISelLowering that is exposed only when
you have a dmask == 0x1. Fix this by adding in an explicit check to
ensure we don't do the UBSan detected shl << 32.

llvm-svn: 345962

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 66eb9bb..55b1a87 100644 (file)
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -8799,7 +8799,7 @@ SDNode *SITargetLowering::adjustWritemask(MachineSDNode *&Node,
 
     // Set which texture component corresponds to the lane.
     unsigned Comp;
-    for (unsigned i = 0, Dmask = OldDmask; i <= Lane; i++) {
+    for (unsigned i = 0, Dmask = OldDmask; (i <= Lane) && (Dmask != 0); i++) {
       Comp = countTrailingZeros(Dmask);
       Dmask &= ~(1 << Comp);
     }