diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -10862,7 +10862,7 @@
 /// Helper function for adjustWritemask
 static unsigned SubIdx2Lane(unsigned Idx) {
   switch (Idx) {
-  default: return 0;
+  default: return ~0u;
   case AMDGPU::sub0: return 0;
   case AMDGPU::sub1: return 1;
   case AMDGPU::sub2: return 2;
@@ -10922,6 +10922,8 @@
     // in OldDmask, so it can be any of X,Y,Z,W; Lane==1 is the second bit
     // set, etc.
     Lane = SubIdx2Lane(I->getConstantOperandVal(1));
+    if (Lane == ~0u)
+      return Node;
 
     // Check if the use is for the TFE/LWE generated result at VGPRn+1.
     if (UsesTFC && Lane == TFCLane) {