[llvm] [VPlan] Add initial loop-invariant code motion transform. (PR #107894)

[via llvm-commits]

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@@ -971,6 +971,41 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     return R.getVPSingleValue()->replaceAllUsesWith(A);
 }
 
+/// Move loop-invariant recipes out of the vector loop region in \p Plan.
+static void licm(VPlan &Plan) {
+  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
+  VPBasicBlock *Preheader =
+      cast<VPBasicBlock>(LoopRegion->getSinglePredecessor());
+
+  // Return true if we do not know how to (mechanically) hoist a given recipe
+  // out of a loop region. Does not address legality concerns such as aliasing
+  // or speculation safety.
+  auto CannotHoistRecipe = [](VPRecipeBase &R) {
+    // Allocas cannot be hoisted.
+    auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
+    return RepR && RepR->getOpcode() == Instruction::Alloca;
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ayalz wrote:

nit: match?

https://github.com/llvm/llvm-project/pull/107894