[llvm] [VPlan] Materialize VF and VFxUF using VPInstructions. (PR #152879)

[Florian Hahn via llvm-commits]

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@@ -3335,6 +3335,33 @@ void VPlanTransforms::materializeVectorTripCount(VPlan &Plan,
   VectorTC.replaceAllUsesWith(Res);
 }
 
+void VPlanTransforms::materializeVFAndVFxUF(VPlan &Plan, VPBasicBlock *VectorPH,
+                                            ElementCount VFEC) {
+  VPBuilder Builder(VectorPH, VectorPH->begin());
+  Type *TCTy = VPTypeAnalysis(Plan).inferScalarType(Plan.getTripCount());
+  VPValue &VF = Plan.getVF();
+  VPValue &VFxUF = Plan.getVFxUF();
+  if (VF.getNumUsers()) {
+    VPValue *RuntimeVF = Builder.createElementCount(TCTy, VFEC);
+    if (any_of(VF.users(), [&VF](VPUser *U) { return !U->usesScalars(&VF); })) {
+      auto *BC = Builder.createNaryOp(VPInstruction::Broadcast, RuntimeVF);
+      VF.replaceUsesWithIf(
+          BC, [&VF](VPUser &U, unsigned) { return !U.usesScalars(&VF); });
+    }
+    VF.replaceAllUsesWith(RuntimeVF);
+
+    VPValue *UF = Plan.getOrAddLiveIn(ConstantInt::get(TCTy, Plan.getUF()));
+    auto *MulByUF = Plan.getUF() == 1 ? RuntimeVF
+                                      : Builder.createNaryOp(Instruction::Mul,
+                                                             {RuntimeVF, UF});
+    VFxUF.replaceAllUsesWith(MulByUF);
+    return;
+  }
+
+  VPValue *RuntimeVFxUF = Builder.createElementCount(TCTy, VFEC * Plan.getUF());
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fhahn wrote:

Not in all cases, e.g. if the canonical IV and its increment can be completely be removed. If it won't get used, VPlan DCE can remove it. The reason we check for users of VF is that we compute things in slightly different order if we need to provide a value for the runtime VF

https://github.com/llvm/llvm-project/pull/152879