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

[Matthew Devereau via llvm-commits]

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@@ -2287,6 +2288,46 @@ 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;
+
+  Value *StoreVal;
+  if (!match(DepInst,
+             m_Intrinsic<Intrinsic::masked_store>(m_Value(StoreVal), m_Value(),
+                                                  m_Value(), m_Specific(Mask))))
+    return false;
+
+  Value *OpToForward = nullptr;
+  if (match(StoreVal, m_MaskedLoad(m_Value(), m_Value(), m_Specific(Mask),
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MDevereau wrote:

As it stands I don't believe said InstCombine exists: https://godbolt.org/z/K835KeW1d. I think what you're proposing is a more elegant way to reach the end result though.

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