[DAGCombiner] Add test exposing bug in DAG combine.

Adds a test in X86, exposing a bug in DAG combine eliminating stores that
are the same value but no the same address space.

Differential Revision: https://reviews.llvm.org/D102243

llvm/test/CodeGen/X86/dagcombine-dead-store.ll

@@ -0,0 +1,87 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=i686-pc-linux | FileCheck %s
+
+; Checks that the stores aren't eliminated by the DAG combiner, because the address
+; spaces are different. In X86, we're checking this for the non-zero address space :fs.
+; The test's 'same' and 'diff' notation depicts whether the pointer value is the same
+; or different.
+
+; FIXME: DAG combine incorrectly eliminates store if pointer is of same value.
+
+define i32 @copy_fs_same() {
+; CHECK-LABEL: copy_fs_same:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movl 1, %eax
+; CHECK-NEXT:    retl
+entry:
+   %0 = load i32, i32* inttoptr (i64 1 to i32*), align 4
+  store i32 %0, i32 addrspace(257)* inttoptr (i64 1 to i32 addrspace(257)*), align 4
+  ret i32 %0
+}
+
+define i32 @copy_fs_diff() {
+; CHECK-LABEL: copy_fs_diff:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movl 1, %eax
+; CHECK-NEXT:    movl %eax, %fs:2
+; CHECK-NEXT:    retl
+entry:
+   %0 = load i32, i32* inttoptr (i64 1 to i32*), align 4
+  store i32 %0, i32 addrspace(257)* inttoptr (i64 2 to i32 addrspace(257)*), align 4
+  ret i32 %0
+}
+
+define void @output_fs_same(i32 %v) {
+; CHECK-LABEL: output_fs_same:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movl %eax, 1
+; CHECK-NEXT:    retl
+entry:
+  store i32 %v, i32* inttoptr (i64 1 to i32*), align 4
+  store i32 %v, i32 addrspace(257)* inttoptr (i64 1 to i32 addrspace(257)*), align 4
+  ret void
+}
+
+define void @output_fs_diff(i32 %v) {
+; CHECK-LABEL: output_fs_diff:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movl %eax, 1
+; CHECK-NEXT:    movl %eax, %fs:2
+; CHECK-NEXT:    retl
+entry:
+  store i32 %v, i32* inttoptr (i64 1 to i32*), align 4
+  store i32 %v, i32 addrspace(257)* inttoptr (i64 2 to i32 addrspace(257)*), align 4
+  ret void
+}
+
+define void @output_indexed_fs_same(i32 %v, i32* %b) {
+; CHECK-LABEL: output_indexed_fs_same:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; CHECK-NEXT:    movl %eax, 168(%ecx)
+; CHECK-NEXT:    retl
+  %p = getelementptr i32, i32* %b, i64 42
+  %pa = addrspacecast i32* %p to i32 addrspace(257)*
+  store i32 %v, i32* %p, align 4
+  store i32 %v, i32 addrspace(257)* %pa, align 4
+  ret void
+}
+
+define void @output_indexed_fs_diff(i32 %v, i32* %b) {
+; CHECK-LABEL: output_indexed_fs_diff:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; CHECK-NEXT:    movl %eax, 168(%ecx)
+; CHECK-NEXT:    movl %eax, %fs:184(%ecx)
+; CHECK-NEXT:    retl
+  %p = getelementptr i32, i32* %b, i64 42
+  %pa = addrspacecast i32* %p to i32 addrspace(257)*
+  %pad = getelementptr i32, i32 addrspace(257)* %pa, i64 4
+  store i32 %v, i32* %p, align 4
+  store i32 %v, i32 addrspace(257)* %pad, align 4
+  ret void
+}