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

[Matt Arsenault via llvm-commits]

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@@ -15527,6 +15532,28 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
     break;
   }
 
+  if (TLI.isNarrowingProfitable(N0.getNode(), SrcVT, VT)) {
+    switch (N0.getOpcode()) {
+    case ISD::ADD:
+    case ISD::SUB:
+    case ISD::MUL:
+    case ISD::AND:
+    case ISD::OR:
+    case ISD::XOR:
+      if (!(N0.hasOneUse() && VT.isScalarInteger()))
+        break;
+      if (LegalOperations && !TLI.isOperationLegal(N0.getOpcode(), VT))
+        break;
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arsenm wrote:

Swap this check with the isNarowingProfitable above? This is the simpler condition

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