[llvm] [AMDGPU] Allow sinking of free vector ops (PR #109172)

[Matt Arsenault via llvm-commits]

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@@ -6010,8 +6010,94 @@ bool AMDGPUTargetLowering::shouldSinkOperands(
     if (any_of(Ops, [&](Use *U) { return U->get() == Op.get(); }))
       continue;
 
+    // This helps using several modifiers (abs and neg) more often.
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arsenm wrote:

Looking for all the free operations is already in TargetTransformInfo. I think all of these IR hooks in TargetLowering for CodeGenPrepare are for historical reasons. Can you try just moving it there, and checking for free costs? 

https://github.com/llvm/llvm-project/pull/109172