[X86] Add test case simplified from PR51175. NFC

Author: topperc

llvm/test/CodeGen/X86/pr51175.ll

@@ -0,0 +1,29 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
+
+; The and with -9 has multiple users which prevents
+; SimplifyDemandedBits from touching it. The truncate only
+; demands the lower 8 bits. X86ISelDAGToDAG.cpp wants form
+; a test instruction from the icmp+trunc+and, but needs to
+; mask the -9 to 8 bits since SimplifyDemandedBits didn't.
+
+define i32 @foo(i16 signext %0, i32 %1, i32* nocapture %2) {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    incl %edi
+; CHECK-NEXT:    movl %edi, %eax
+; CHECK-NEXT:    andl $65527, %eax # imm = 0xFFF7
+; CHECK-NEXT:    movl %eax, (%rdx)
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    testl $-9, %edi
+; CHECK-NEXT:    cmovel %esi, %eax
+; CHECK-NEXT:    retq
+  %4 = add i16 %0, 1
+  %5 = and i16 %4, -9
+  %6 = zext i16 %5 to i32
+  store i32 %6, i32* %2, align 4
+  %7 = trunc i16 %5 to i8
+  %8 = icmp eq i8 %7, 0
+  %9 = select i1 %8, i32 %1, i32 0
+  ret i32 %9
+}