[X86] Add test for PR39926; NFC

The test file shows a case where the avoid store forwarding block
pass misses to copy a range (-1..1) when the load displacement
changes sign.

Baseline test for D55485.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348712 91177308-0d34-0410-b5e6-96231b3b80d8

Author: nikic

test/CodeGen/X86/pr39926.ll

@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=avx | FileCheck %s
+define i8 @test_offset(i8* %base) {
+; CHECK-LABEL: test_offset:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    movb $0, 7(%rdi)
+; CHECK-NEXT:    movw $0, 5(%rdi)
+; CHECK-NEXT:    movl $0, 1(%rdi)
+; CHECK-NEXT:    movzwl -4(%rdi), %eax
+; CHECK-NEXT:    movw %ax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb -2(%rdi), %al
+; CHECK-NEXT:    movb %al, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movl 1(%rdi), %eax
+; CHECK-NEXT:    movl %eax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movzwl 5(%rdi), %eax
+; CHECK-NEXT:    movw %ax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb 7(%rdi), %al
+; CHECK-NEXT:    movb %al, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movl 8(%rdi), %eax
+; CHECK-NEXT:    movl %eax, -{{[0-9]+}}(%rsp)
+; CHECK-NEXT:    movb -{{[0-9]+}}(%rsp), %al
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+entry:
+  %z = alloca [128 x i8], align 16
+  %gep0 = getelementptr inbounds i8, i8* %base, i64 7
+  store volatile i8 0, i8* %gep0
+  %gep1 = getelementptr inbounds i8, i8* %base, i64 5
+  %bc1 = bitcast i8* %gep1 to i16*
+  store volatile i16 0, i16* %bc1
+  %gep2 = getelementptr inbounds i8, i8* %base, i64 1
+  %bc2 = bitcast i8* %gep2 to i32*
+  store volatile i32 0, i32* %bc2
+
+  %y1 = getelementptr inbounds i8, i8* %base, i64 -4
+  %y2 = bitcast [128 x i8]* %z to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %y2, i8* %y1, i64 16, i1 false)
+
+  %gep4 = getelementptr inbounds [128 x i8], [128 x i8]* %z, i64 0, i64 4
+  %ret = load i8, i8* %gep4
+  ret i8 %ret
+}
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i1)