[llvm] [DAGCombine] Propagate truncate to operands (PR #98666)

[Justin Fargnoli via llvm-commits]

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@@ -5797,7 +5797,7 @@ SDValue DAGCombiner::hoistLogicOpWithSameOpcodeHands(SDNode *N) {
   }
 
   // logic_op (truncate x), (truncate y) --> truncate (logic_op x, y)
-  if (HandOpcode == ISD::TRUNCATE) {
+  if (HandOpcode == ISD::TRUNCATE && !TLI.shouldReduceRegisterPressure()) {
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justinfargnoli wrote:

I've added a comment. 

I added support for `TLI.isTruncateFree(EVT, EVT)`. 

I'm holding off on implementing `TLI.ZExtFree()` because it isn't necessary for this optimization. 

https://github.com/llvm/llvm-project/pull/98666