[PATCH] D122095: [VPlan] Place VPExpandSCEVRecipe in pre-header.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: gilr, Ayal, rengolin.
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After D121624 <https://reviews.llvm.org/D121624> models the pre-header in VPlan, VPExpandSCEVRecipes can be
placed there. This ensures SCEV expansion happens before modifying the
CFG during VPlan execution, when CFG is incomplete.

Depends on D121624 <https://reviews.llvm.org/D121624>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122095

Files:
  llvm/lib/Transforms/Vectorize/VPlan.cpp
  llvm/lib/Transforms/Vectorize/VPlan.h
  llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
  llvm/test/Transforms/LoopVectorize/vplan-printing.ll


Index: llvm/test/Transforms/LoopVectorize/vplan-printing.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/vplan-printing.ll
+++ llvm/test/Transforms/LoopVectorize/vplan-printing.ll
@@ -418,6 +418,7 @@
 ; CHECK-NEXT: Live-in vp<%0> = vector-trip-count
 ; CHECK-EMPTY:
 ; CHECK-NEXT: vector.ph:
+; CHECK-NEXT:   EMIT vp<[[EXP_SCEV:%.+]]> = EXPAND SCEV (1 + (%y /u 492802768830814060))<nuw><nsw>
 ; CHECK-NEXT: Successor(s): vector loop
 ; CHECK-EMPTY:
 ; CHECK-NEXT: <x1> vector loop: {
@@ -426,7 +427,6 @@
 ; CHECK-NEXT:     WIDEN-INDUCTION\l" +
 ; CHECK-NEXT:     "  %iv = phi %iv.next, 0\l" +
 ; CHECK-NEXT:     "  ir<%v2>
-; CHECK-NEXT:     EMIT vp<[[EXP_SCEV:%.+]]> = EXPAND SCEV (1 + (%y /u 492802768830814060))<nuw><nsw>
 ; CHECK-NEXT:     vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[CAN_IV]]>, ir<0>, vp<[[EXP_SCEV]]>
 ; CHECK-NEXT:     WIDEN ir<%v3> = add ir<%v2>, ir<1>
 ; CHECK-NEXT:     REPLICATE ir<%gep> = getelementptr ir<%ptr>, vp<[[STEPS]]>
Index: llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -436,12 +436,9 @@
         IV->getStartValue(), Step, TruncI ? TruncI->getType() : nullptr);
 
     HeaderVPBB->insert(Steps, HeaderVPBB->getFirstNonPhi());
-    if (Step->getDef()) {
-      // TODO: Place the step in the preheader, once it is explicitly modeled in
-      // VPlan.
-      HeaderVPBB->insert(cast<VPRecipeBase>(Step->getDef()),
-                         HeaderVPBB->getFirstNonPhi());
-    }
+    if (Step->getDef())
+      Plan.getEntry()->getEntryBasicBlock()->appendRecipe(
+          cast<VPRecipeBase>(Step->getDef()));
 
     // If there are no vector users of IV, simply update all users to use Step
     // instead.
Index: llvm/lib/Transforms/Vectorize/VPlan.h
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlan.h
+++ llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1806,9 +1806,6 @@
 };
 
 /// Recipe to expand a SCEV expression.
-/// TODO: Currently the recipe always expands the expression in the loop
-/// pre-header, but the recipe is currently placed in the header; place it in
-/// the pre-header once the latter is modeled in VPlan as a VPBasicBlock.
 class VPExpandSCEVRecipe : public VPRecipeBase, public VPValue {
   const SCEV *Expr;
   ScalarEvolution &SE;
Index: llvm/lib/Transforms/Vectorize/VPlan.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlan.cpp
+++ llvm/lib/Transforms/Vectorize/VPlan.cpp
@@ -1463,7 +1463,7 @@
       State.CFG.VectorPreHeader->getModule()->getDataLayout();
   SCEVExpander Exp(SE, DL, "induction");
   Value *Res = Exp.expandCodeFor(Expr, Expr->getType(),
-                                 State.CFG.VectorPreHeader->getTerminator());
+                                 &*State.Builder.GetInsertPoint());
 
   for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
     State.set(this, Res, Part);


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