[llvm] [VPlan] Expand VPWidenPointerInductionRecipe into separate recipes (PR #148274)

[Luke Lau via llvm-commits]

================
@@ -2679,6 +2680,102 @@ expandVPWidenIntOrFpInduction(VPWidenIntOrFpInductionRecipe *WidenIVR,
   WidenIVR->replaceAllUsesWith(WidePHI);
 }
 
+/// Expand a VPWidenPointerInductionRecipe into executable recipes, for the
+/// initial value, phi and backedge value. In the following example:
+///
+///  <x1> vector loop: {
+///    vector.body:
+///      EMIT ir<%ptr.iv> = WIDEN-POINTER-INDUCTION %start, %step, %vf
+///      ...
+///      EMIT branch-on-count ...
+///  }
+///
+/// WIDEN-POINTER-INDUCTION will get expanded to:
+///
+///  <x1> vector loop: {
+///    vector.body:
+///      EMIT-SCALAR %pointer.phi = phi %start, %ptr.ind
+///      EMIT %mul = mul %stepvector, %step
+///      EMIT %vector.gep = ptradd %pointer.phi, %mul
+///      ...
+///      EMIT %ptr.ind = ptradd %pointer.phi, %vf
+///      EMIT branch-on-count ...
+///  }
+static void expandVPWidenPointerInduction(VPWidenPointerInductionRecipe *R,
+                                          VPTypeAnalysis &TypeInfo) {
+  VPlan *Plan = R->getParent()->getPlan();
+
+  assert(R->getInductionDescriptor().getKind() ==
+             InductionDescriptor::IK_PtrInduction &&
+         "Not a pointer induction according to InductionDescriptor!");
+  assert(TypeInfo.inferScalarType(R)->isPointerTy() && "Unexpected type.");
+  assert(!R->onlyScalarsGenerated(Plan->hasScalableVF()) &&
+         "Recipe should have been replaced");
+
+  unsigned CurrentPart = R->getCurrentPart();
+
+  VPBuilder Builder(R);
+  DebugLoc DL = R->getDebugLoc();
+
+  // Build a pointer phi
+  VPPhi *Phi;
+  if (CurrentPart == 0) {
+    Phi = Builder.createScalarPhi({R->getStartValue()}, DL, "pointer.phi");
+  } else {
+    // The recipe has been unrolled. In that case, fetch the single pointer phi
+    // shared among all unrolled parts of the recipe.
+    auto *PtrAdd = cast<VPInstruction>(R->getFirstUnrolledPartOperand());
+    Phi = cast<VPPhi>(PtrAdd->getOperand(0)->getDefiningRecipe());
+  }
+
+  Builder.setInsertPoint(R->getParent(), R->getParent()->getFirstNonPhi());
+
+  // A pointer induction, performed by using a gep
+  Type *PhiType = TypeInfo.inferScalarType(R->getStepValue());
----------------
lukel97 wrote:

The type of the phi is indeed a pointer type, this name is just copied over from the existing execute code. It's actually the type of the offset used in the ptradd. I'll go ahead and rename it.

https://github.com/llvm/llvm-project/pull/148274