[llvm] [IR] Add storermw instruction (PR #207048)

[Matt Arsenault via llvm-commits]

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@@ -1981,6 +1981,18 @@ class IRBuilderBase {
         new AtomicRMWInst(Op, Ptr, Val, *Align, Ordering, SSID, Elementwise));
   }
 
+  StoreRMWInst *CreateStoreRMW(AtomicRMWInst::BinOp Op, Value *Ptr, Value *Val,
+                               MaybeAlign Align, AtomicOrdering Ordering,
+                               SyncScope::ID SSID = SyncScope::System,
+                               bool Elementwise = false) {
+    if (!Align) {
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arsenm wrote:

No MaybeAlign. IMO MaybeAlign should not exist and the existing default-to-typesize-align should be ripped out of the IR and made an assembler-only convention 

https://github.com/llvm/llvm-project/pull/207048