[llvm] [SelectionDAG] Treat CopyFromReg as freezing the value (PR #85932)

[Björn Pettersson via llvm-commits]

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@@ -202,13 +202,27 @@ define <4 x i32> @freeze_add_vec(<4 x i32> %a0) nounwind {
 define <4 x i32> @freeze_add_vec_undef(<4 x i32> %a0) nounwind {
 ; X86-LABEL: freeze_add_vec_undef:
 ; X86:       # %bb.0:
+; X86-NEXT:    pushl %ebp
+; X86-NEXT:    movl %esp, %ebp
+; X86-NEXT:    andl $-16, %esp
+; X86-NEXT:    subl $32, %esp
+; X86-NEXT:    movl %eax, {{[0-9]+}}(%esp)
+; X86-NEXT:    movl $3, {{[0-9]+}}(%esp)
+; X86-NEXT:    movl $2, {{[0-9]+}}(%esp)
+; X86-NEXT:    movl $1, (%esp)
+; X86-NEXT:    paddd (%esp), %xmm0
 ; X86-NEXT:    paddd {{\.?LCPI[0-9]+_[0-9]+}}, %xmm0
-; X86-NEXT:    paddd {{\.?LCPI[0-9]+_[0-9]+}}, %xmm0
+; X86-NEXT:    movl %ebp, %esp
+; X86-NEXT:    popl %ebp
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bjope wrote:

The discussion here https://discourse.llvm.org/t/what-are-we-allowed-to-do-with-freeze-undef-in-selectiondag/78175/11 was started when I looked at this.

https://github.com/llvm/llvm-project/pull/85932