[llvm] [GVN] Teach GVN simple masked load/store forwarding (PR #157689)

[Ramkumar Ramachandra via llvm-commits]

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@@ -2287,6 +2288,50 @@ bool GVNPass::processLoad(LoadInst *L) {
   return true;
 }
 
+// Attempt to process masked loads which have loaded from
+// masked stores with the same mask
+bool GVNPass::processMaskedLoad(IntrinsicInst *I) {
+  Value *Mask = I->getOperand(2);
+  Value *Passthrough = I->getOperand(3);
+
+  MemDepResult Dep = MD->getDependency(I);
+  Instruction *DepInst = Dep.getInst();
+  if (!DepInst || !Dep.isLocal())
+    return false;
+
+  auto *MaskedStore = dyn_cast<IntrinsicInst>(DepInst);
+  if (!MaskedStore || MaskedStore->getIntrinsicID() != Intrinsic::masked_store)
+    return false;
+
+  auto StoreMask = MaskedStore->getOperand(3);
+  if (StoreMask != Mask)
+    return false;
+
+  Value *OpToForward =
+      AvailableValue::get(MaskedStore->getOperand(0)).getSimpleValue();
+  if (auto *LoadToForward = dyn_cast<IntrinsicInst>(OpToForward);
+      LoadToForward &&
+      LoadToForward->getIntrinsicID() == Intrinsic::masked_load) {
+    // For MaskedLoad->MaskedStore->MaskedLoad, the mask must be the same for
+    // all three instructions. The Passthrough on the two loads must also be the
+    // same.
+    if (LoadToForward->getOperand(2) != Mask ||
+        LoadToForward->getOperand(3) != Passthrough)
+      return false;
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artagnon wrote:

Kindly use m_Intrinsic and m_Specific from PatternMatch.

https://github.com/llvm/llvm-project/pull/157689