[llvm] [AMDGPU][DAG] Enable ganging up of memcpy loads/stores for AMDGPU (PR #96185)

[Matt Arsenault via llvm-commits]

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@@ -67,6 +67,9 @@ AMDGPUTargetLowering::AMDGPUTargetLowering(const TargetMachine &TM,
   MaxStoresPerMemcpy = MaxStoresPerMemcpyOptSize = ~0U;
   MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = ~0U;
 
+  // Enable ganging up loads and stores in the memcpy DAG lowering.
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arsenm wrote:

I mean it's a problem when things get added for only a single target out of fear of regressing anything else. Also I don't see what target property would correspond to a value here. It's in terms of store count, not even bytes or load width or anything. I'm saying this is a bad API 

https://github.com/llvm/llvm-project/pull/96185