[llvm] [X86] Enable alias analysis (AA) during codegen (PR #123787)

[Benjamin Maxwell via llvm-commits]

================
@@ -13,15 +13,10 @@ target triple = "x86_64-apple-macosx10.8.0"
 ; should have been changed into movzbl instead.
 ; CHECK-LABEL: foo1
 ; load:
-; BWON:  movzbl
-; BWOFF: movb
-; store:
-; CHECK: movb
-; load:
-; BWON: movzbl
-; BWOFF: movb
+; BWON:  movzwl
+; BWOFF: movw
----------------
MacDue wrote:

Yes, it appears the two `movzbl` and `movb` have been merged into one `movzwl` and one `movw`:
**Before:**
```
LBB0_1:                                 ## %a4
                                        ## =>This Inner Loop Header: Depth=1
	movzbl	(%rsi), %eax
	movb	%al, (%rdx)
	movzbl	1(%rsi), %eax
	movb	%al, 1(%rdx)
	addq	$8, %rdx
	decl	%edi
	jne	LBB0_1
```
**After:**
```
LBB0_1:                                 ## %a4
                                        ## =>This Inner Loop Header: Depth=1
	movzwl	(%rsi), %eax
	movw	%ax, (%rdx)
	addq	$8, %rdx
	decl	%edi
	jne	LBB0_1
```

https://github.com/llvm/llvm-project/pull/123787