[llvm] [LLVM][DAGCombiner] Look through freeze when combining extensions of loads (PR #175022)

[David Sherwood via llvm-commits]

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@@ -14552,35 +14556,49 @@ static SDValue tryToFoldExtOfLoad(SelectionDAG &DAG, DAGCombiner &Combiner,
   // TODO: isFixedLengthVector() should be removed and any negative effects on
   // code generation being the result of that target's implementation of
   // isVectorLoadExtDesirable().
-  if ((LegalOperations || VT.isFixedLengthVector() ||
-       !cast<LoadSDNode>(N0)->isSimple()) &&
-      !TLI.isLoadExtLegal(ExtLoadType, VT, N0.getValueType()))
+  if ((LegalOperations || VT.isFixedLengthVector() || !Load->isSimple()) &&
+      !TLI.isLoadExtLegal(ExtLoadType, VT, Load->getValueType(0)))
     return {};
 
   bool DoXform = true;
   SmallVector<SDNode *, 4> SetCCs;
-  if (!N0.hasOneUse())
-    DoXform = ExtendUsesToFormExtLoad(VT, N, N0, ExtOpc, SetCCs, TLI);
+  if (!Load->hasOneUse() || (Frozen && !N0->hasOneUse()))
+    DoXform = ExtendUsesToFormExtLoad(VT, N, Frozen ? N0 : SDValue(Load, 0),
+                                      ExtOpc, SetCCs, TLI);
   if (VT.isVector())
     DoXform &= TLI.isVectorLoadExtDesirable(SDValue(N, 0));
   if (!DoXform)
     return {};
 
-  LoadSDNode *LN0 = cast<LoadSDNode>(N0);
-  SDValue ExtLoad = DAG.getExtLoad(ExtLoadType, SDLoc(LN0), VT, LN0->getChain(),
-                                   LN0->getBasePtr(), N0.getValueType(),
-                                   LN0->getMemOperand());
-  Combiner.ExtendSetCCUses(SetCCs, N0, ExtLoad, ExtOpc);
+  SDLoc DL(Load);
+  SDValue ExtLoad =
+      DAG.getExtLoad(ExtLoadType, DL, VT, Load->getChain(), Load->getBasePtr(),
+                     Load->getValueType(0), Load->getMemOperand());
   // If the load value is used only by N, replace it via CombineTo N.
-  bool NoReplaceTrunc = SDValue(LN0, 0).hasOneUse();
-  Combiner.CombineTo(N, ExtLoad);
+  bool NoReplaceTrunc = Frozen ? N0->hasOneUse() : Load->hasOneUse();
+  SDValue Res;
+  if (Frozen) {
+    Res = DAG.getFreeze(ExtLoad);
+    Res = DAG.getNode(ExtLoadType == ISD::SEXTLOAD ? ISD::AssertSext
+                                                   : ISD::AssertZext,
+                      DL, Res.getValueType(), Res,
+                      DAG.getValueType(Load->getValueType(0).getScalarType()));
+  } else {
+    Res = ExtLoad;
+  }
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david-arm wrote:

Done

https://github.com/llvm/llvm-project/pull/175022