[X86] pr40090.ll - add ctlz(x,false) (zero isn't poison) test coverage

Author: RKSimon

llvm/test/CodeGen/X86/pr40090.ll

@@ -21,4 +21,26 @@ define i64 @foo(i64 %x, i64 %y) {
   ret i64 %7
 }
 
+define i64 @bar(i64 %x, i64 %y) {
+; CHECK-LABEL: bar:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl $127, %ecx
+; CHECK-NEXT:    movl $127, %eax
+; CHECK-NEXT:    bsrq %rdi, %rax
+; CHECK-NEXT:    xorq $64, %rax
+; CHECK-NEXT:    bsrq %rsi, %rcx
+; CHECK-NEXT:    cmoveq %rax, %rcx
+; CHECK-NEXT:    movl $63, %eax
+; CHECK-NEXT:    subq %rcx, %rax
+; CHECK-NEXT:    retq
+  %1 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 false)
+  %2 = xor i64 %1, 127
+  %3 = tail call i64 @llvm.ctlz.i64(i64 %y, i1 false)
+  %4 = xor i64 %3, 63
+  %5 = icmp eq i64 %y, 0
+  %6 = select i1 %5, i64 %2, i64 %4
+  %7 = sub nsw i64 63, %6
+  ret i64 %7
+}
+
 declare i64 @llvm.ctlz.i64(i64, i1)