[llvm] [DAG] visitFREEZE - replace multiple frozen/unfrozen uses of an SDValue with just the frozen node (PR #150017)

[Simon Pilgrim via llvm-commits]

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@@ -490,18 +490,19 @@ define i32 @freeze_ashr_exact(i32 %a0) nounwind {
 define i32 @freeze_ashr_exact_extra_use(i32 %a0, ptr %escape) nounwind {
 ; X86-LABEL: freeze_ashr_exact_extra_use:
 ; X86:       # %bb.0:
-; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    sarl $3, %eax
-; X86-NEXT:    movl %eax, (%ecx)
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    sarl $3, %ecx
+; X86-NEXT:    movl %ecx, (%eax)
+; X86-NEXT:    movl %ecx, %eax
 ; X86-NEXT:    sarl $6, %eax
 ; X86-NEXT:    retl
----------------
RKSimon wrote:

DAG still preserves the exact, but instcombine will optimize to:
```ll
define i32 @freeze_ashr_exact_extra_use(i32 %a0, ptr %escape) #0 {
  %a0.fr = freeze i32 %a0
  %x = ashr i32 %a0.fr, 3
  %z = ashr i32 %a0.fr, 9
  store i32 %x, ptr %escape, align 4
  ret i32 %z
}
```

https://github.com/llvm/llvm-project/pull/150017