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

[Justin Fargnoli via llvm-commits]

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@@ -2975,6 +2975,8 @@ class TargetLoweringBase {
     return isTruncateFree(Val.getValueType(), VT2);
   }
 
+  virtual bool shouldReduceRegisterPressure() const { return false; }
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justinfargnoli wrote:

> This is essentially the same thing as aggressivelyPreferBuildVectorSources, and isNarrowingProfitable

Thank you for pointing this out! I agree that `isNarrowingProfitable()` is the right way forward. 

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