[llvm] [AMDGPU] Filter candidates of LiveRegOptimizer for profitable cases (PR #124624)

[Jeffrey Byrnes via llvm-commits]

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@@ -125,8 +131,210 @@ class LiveRegOptimizer {
     return LK.first != TargetLoweringBase::TypeLegal;
   }
 
-  LiveRegOptimizer(Module &Mod, const GCNSubtarget &ST)
-      : Mod(Mod), DL(Mod.getDataLayout()), ST(ST),
+  // Filtering based on operation or its cost.
+  // If an operation incurs high enough cost or natively work on
+  // vector of illegal type, ie. v2i8, then it makes sense to try
+  // to coerce them as packed VGPR across BB.
+  bool shouldReplaceByOp(Instruction *II) {
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jrbyrnes wrote:

I think we can just delete this cost model in favor of the whitelist -- should be able to remove dependency on TTI too

https://github.com/llvm/llvm-project/pull/124624