diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -5446,6 +5446,9 @@
       ConstantSDNode *C = dyn_cast<ConstantSDNode>(N0.getOperand(1));
       if (!C) break;
       uint64_t Mask = C->getZExtValue();
+      // We may have looked through a truncate so mask off any bits that
+      // shouldn't be part of the compare.
+      Mask &= maskTrailingOnes<uint64_t>(CmpVT.getScalarSizeInBits());
 
       // Check if we can replace AND+IMM64 with a shift. This is possible for
       // masks/ like 0xFF000000 or 0x00FFFFFF and if we care only about the zero
diff --git a/llvm/test/CodeGen/X86/pr51175.ll b/llvm/test/CodeGen/X86/pr51175.ll
--- a/llvm/test/CodeGen/X86/pr51175.ll
+++ b/llvm/test/CodeGen/X86/pr51175.ll
@@ -15,7 +15,7 @@
 ; CHECK-NEXT:    andl $65527, %eax # imm = 0xFFF7
 ; CHECK-NEXT:    movl %eax, (%rdx)
 ; CHECK-NEXT:    xorl %eax, %eax
-; CHECK-NEXT:    testl $-9, %edi
+; CHECK-NEXT:    testb $-9, %dil
 ; CHECK-NEXT:    cmovel %esi, %eax
 ; CHECK-NEXT:    retq
   %4 = add i16 %0, 1