[llvm] 5f1eb74 - [VPlan] Place VPExpandSCEVRecipe in pre-header.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-04-10T10:26:20+02:00
New Revision: 5f1eb7485077eb295fc17568c0abcf7799b0ade8

URL: https://github.com/llvm/llvm-project/commit/5f1eb7485077eb295fc17568c0abcf7799b0ade8
DIFF: https://github.com/llvm/llvm-project/commit/5f1eb7485077eb295fc17568c0abcf7799b0ade8.diff

LOG: [VPlan] Place VPExpandSCEVRecipe in pre-header.

After 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.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D122095

Added: 
    

Modified: 
    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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/VPlan.cpp b/llvm/lib/Transforms/Vectorize/VPlan.cpp
index d531c7a6a761b..48877850184c3 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlan.cpp
@@ -1474,9 +1474,8 @@ void VPExpandSCEVRecipe::execute(VPTransformState &State) {
   const DataLayout &DL = State.CFG.PrevBB->getModule()->getDataLayout();
   SCEVExpander Exp(SE, DL, "induction");
 
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
-  Value *Res =
-      Exp.expandCodeFor(Expr, Expr->getType(), VectorPH->getTerminator());
+  Value *Res = Exp.expandCodeFor(Expr, Expr->getType(),
+                                 &*State.Builder.GetInsertPoint());
 
   for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
     State.set(this, Res, Part);

diff  --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index 683613097ef4f..0430264de54ac 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1805,9 +1805,6 @@ class VPWidenMemoryInstructionRecipe : public VPRecipeBase, public VPValue {
 };
 
 /// 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;

diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index cbef53540bfb2..8f0c7cafc7c21 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -437,12 +437,9 @@ void VPlanTransforms::optimizeInductions(VPlan &Plan, ScalarEvolution &SE) {
         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.

diff  --git a/llvm/test/Transforms/LoopVectorize/vplan-printing.ll b/llvm/test/Transforms/LoopVectorize/vplan-printing.ll
index ab61a0e4437a8..5ba13c1777ea7 100644
--- a/llvm/test/Transforms/LoopVectorize/vplan-printing.ll
+++ b/llvm/test/Transforms/LoopVectorize/vplan-printing.ll
@@ -418,6 +418,7 @@ define void @print_expand_scev(i64 %y, i8* %ptr) {
 ; 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 @@ define void @print_expand_scev(i64 %y, i8* %ptr) {
 ; 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]]>