[llvm] [LoopVectorize] Widen selected-base loads with masked loads (PR #213227)

[David Sherwood via llvm-commits]

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@@ -57,6 +57,93 @@ static std::optional<int64_t> getConstantStride(VPValue *Addr, Type *AccessTy,
   return getStrideFromAddRec(AddRec, L, AccessTy, /*Ptr=*/nullptr, PSE);
 }
 
+namespace {
+
+struct SelectedBaseLoadPattern {
+  VPInstruction *Addr;
+  SmallVector<VPValue *> GEPOperands;
+  VPValue *Cond;
+  VPValue *TrueBase;
+  VPValue *FalseBase;
+};
+
+/// Match a load through a GEP whose base pointer is selected per iteration
+/// between two loop-invariant candidates:
+///
+///   load (gep (select Cond, TrueBase, FalseBase), Indices...)
+///
+/// Legality, stride and profitability are checked separately by the caller.
+static std::optional<SelectedBaseLoadPattern>
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david-arm wrote:

Pattern matches are typically added to VPlanPatternMatchers.h

https://github.com/llvm/llvm-project/pull/213227