[llvm] [VPlan] Model address separately. (PR #72164)

[via llvm-commits]

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@@ -397,6 +399,50 @@ Value *VPInstruction::generateInstruction(VPTransformState &State,
     Builder.GetInsertBlock()->getTerminator()->eraseFromParent();
     return CondBr;
   }
+  case VPInstruction::VectorPtr:
+  case VPInstruction::VectorPtrReverse: {
+    // Calculate the pointer for the specific unroll-part.
+    Value *PartPtr = nullptr;
+    bool IsReverse = getOpcode() == VPInstruction::VectorPtrReverse;
+    auto *MemR = cast<VPWidenMemoryInstructionRecipe>(*user_begin());
+    Type *ScalarDataTy =
+        MemR->isStore() ? cast<StoreInst>(&MemR->getIngredient())
+                              ->getValueOperand()
+                              ->getType()
+                        : cast<LoadInst>(&MemR->getIngredient())->getType();
+    // Use i32 for the gep index type when the value is constant,
+    // or query DataLayout for a more suitable index type otherwise.
+    const DataLayout &DL =
+        Builder.GetInsertBlock()->getModule()->getDataLayout();
+    Type *IndexTy = State.VF.isScalable() && (IsReverse || Part > 0)
+                        ? DL.getIndexType(ScalarDataTy->getPointerTo())
+                        : Builder.getInt32Ty();
+    Value *Ptr = State.get(getOperand(0), VPIteration(0, 0));
+    bool InBounds = false;
+    if (auto *GEP = dyn_cast<GetElementPtrInst>(Ptr->stripPointerCasts()))
+      InBounds = GEP->isInBounds();
+    if (IsReverse) {
+      // If the address is consecutive but reversed, then the
+      // wide store needs to start at the last vector element.
+      // RunTimeVF =  VScale * VF.getKnownMinValue()
+      // For fixed-width VScale is 1, then RunTimeVF = VF.getKnownMinValue()
+      Value *RunTimeVF = getRuntimeVF(Builder, IndexTy, State.VF);
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ayalz wrote:

Follow-up should probably use the modelling of VF as VPValue, following the modelling of VFxUF, coupled with unrolling-by-UF as a VPlan-to-VPlan transformation.

https://github.com/llvm/llvm-project/pull/72164