[llvm] [AtomicExpandPass] Match isIdempotentRMW with InstcombineRMW (PR #142277)

[Craig Topper via llvm-commits]

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@@ -85,6 +85,26 @@ define i8 @atomic_max_smin_char(ptr %addr) {
   ret i8 %res
 }
 
+; Idempotent atomicrmw are still canonicalized.
+define i8 @atomic_min_umax_char(ptr %addr) {
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topperc wrote:

Does this provide anything not already covered by the existing `atomic_umin_uint_max`

https://github.com/llvm/llvm-project/pull/142277