[llvm] Make RAUW skip instances where operand is the replacement node (PR #212724)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,18 @@
+; RUN: llc < %s -mtriple=x86_64 -mattr=+avx2 -o /dev/null
+;
+; Verify that CSE-reusing a TokenFactor during broadcast-load combining does not
+; introduce a self-reference while replacing the old chain.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @f18() #0 {
+entry:
+  %0 = load <15 x i64>, ptr null, align 128
+  %shuffle = shufflevector <15 x i64> %0, <15 x i64> zeroinitializer, <16 x i32> <i32 7, i32 6, i32 4, i32 12, i32 9, i32 5, i32 3, i32 5, i32 12, i32 13, i32 0, i32 14, i32 7, i32 8, i32 4, i32 2>
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arsenm wrote:

Can you avoid the UB in the test 

https://github.com/llvm/llvm-project/pull/212724