[llvm] [VPlan] Simplify live-ins early using SCEV. (PR #155304)

Florian Hahn via llvm-commits llvm-commits at lists.llvm.org
Thu Sep 11 08:13:45 PDT 2025


https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/155304

>From 97b6a0c446e4cc59622189ebf0b707210484a109 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Sat, 23 Aug 2025 19:11:00 +0100
Subject: [PATCH 1/2] [VPlan] Simplify live-ins early using SCEV.

Use SCEV to simplify all live-ins during VPlan0 construction. This
enables us to remove special SCEV queries when constructing
VPWidenRecipes and improves results in some cases.

This leads to simplifications in a number of cases in real-world
applications (~250 files changed across LLVM, SPEC, ffmpeg)
---
 .../Transforms/Vectorize/LoopVectorize.cpp    | 28 ++-----------------
 .../Vectorize/VPlanConstruction.cpp           | 19 +++++++++++++
 .../LoopVectorize/iv_outside_user.ll          | 18 ++++--------
 .../reuse-lcssa-phi-scev-expansion.ll         |  2 +-
 .../LoopVectorize/scalable-iv-outside-user.ll | 20 ++-----------
 5 files changed, 30 insertions(+), 57 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index b4acda80cfb93..fa3a84715d8e7 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7792,32 +7792,8 @@ VPWidenRecipe *VPRecipeBuilder::tryToWiden(Instruction *I,
   case Instruction::Shl:
   case Instruction::Sub:
   case Instruction::Xor:
-  case Instruction::Freeze: {
-    SmallVector<VPValue *> NewOps(Operands);
-    if (Instruction::isBinaryOp(I->getOpcode())) {
-      // The legacy cost model uses SCEV to check if some of the operands are
-      // constants. To match the legacy cost model's behavior, use SCEV to try
-      // to replace operands with constants.
-      ScalarEvolution &SE = *PSE.getSE();
-      auto GetConstantViaSCEV = [this, &SE](VPValue *Op) {
-        if (!Op->isLiveIn())
-          return Op;
-        Value *V = Op->getUnderlyingValue();
-        if (isa<Constant>(V) || !SE.isSCEVable(V->getType()))
-          return Op;
-        auto *C = dyn_cast<SCEVConstant>(SE.getSCEV(V));
-        if (!C)
-          return Op;
-        return Plan.getOrAddLiveIn(C->getValue());
-      };
-      // For Mul, the legacy cost model checks both operands.
-      if (I->getOpcode() == Instruction::Mul)
-        NewOps[0] = GetConstantViaSCEV(NewOps[0]);
-      // For other binops, the legacy cost model only checks the second operand.
-      NewOps[1] = GetConstantViaSCEV(NewOps[1]);
-    }
-    return new VPWidenRecipe(*I, NewOps);
-  }
+  case Instruction::Freeze:
+    return new VPWidenRecipe(*I, Operands);
   case Instruction::ExtractValue: {
     SmallVector<VPValue *> NewOps(Operands);
     Type *I32Ty = IntegerType::getInt32Ty(I->getContext());
diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index cef91c15dd873..72423fee790f7 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -20,6 +20,7 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopIterator.h"
 #include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/IR/MDBuilder.h"
 
 #define DEBUG_TYPE "vplan"
@@ -531,12 +532,30 @@ static void addInitialSkeleton(VPlan &Plan, Type *InductionTy, DebugLoc IVDL,
   createExtractsForLiveOuts(Plan, MiddleVPBB);
 }
 
+static void simplifyPlanWithSCEV(VPlan &Plan, ScalarEvolution &SE) {
+  auto SimplifyWithSCEV = [&](VPValue *VPV) -> VPValue * {
+    Value *UV = VPV->getUnderlyingValue();
+    if (!UV || !SE.isSCEVable(UV->getType()))
+      return nullptr;
+    auto *S = SE.getSCEV(UV);
+    if (auto *C = dyn_cast<SCEVConstant>(S))
+      return Plan.getOrAddLiveIn(C->getValue());
+    return nullptr;
+  };
+
+  for (VPValue *LiveIn : Plan.getLiveIns()) {
+    if (auto *Simp = SimplifyWithSCEV(LiveIn))
+      LiveIn->replaceAllUsesWith(Simp);
+  }
+}
+
 std::unique_ptr<VPlan>
 VPlanTransforms::buildVPlan0(Loop *TheLoop, LoopInfo &LI, Type *InductionTy,
                              DebugLoc IVDL, PredicatedScalarEvolution &PSE) {
   PlainCFGBuilder Builder(TheLoop, &LI);
   std::unique_ptr<VPlan> VPlan0 = Builder.buildPlainCFG();
   addInitialSkeleton(*VPlan0, InductionTy, IVDL, PSE, TheLoop);
+  simplifyPlanWithSCEV(*VPlan0, *PSE.getSE());
   return VPlan0;
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll b/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
index 766e7acdfd1c7..246d1d603b88c 100644
--- a/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
+++ b/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
@@ -1081,13 +1081,10 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification(ptr %dst) {
 ; VEC:       [[VECTOR_PH]]:
 ; VEC-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; VEC:       [[VECTOR_BODY]]:
-; VEC-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; VEC-NEXT:    [[TMP0:%.*]] = add i32 [[INDEX]], 0
-; VEC-NEXT:    [[TMP6:%.*]] = add i32 [[INDEX]], 1
+; VEC-NEXT:    [[TMP0:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; VEC-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i16, ptr [[DST]], i32 [[TMP0]]
 ; VEC-NEXT:    store <2 x i16> zeroinitializer, ptr [[TMP1]], align 2
-; VEC-NEXT:    [[TMP5:%.*]] = add i32 [[STEP_2]], [[TMP6]]
-; VEC-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
+; VEC-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[TMP0]], 2
 ; VEC-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[INDEX_NEXT]], 8
 ; VEC-NEXT:    br i1 [[TMP3]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], {{!llvm.loop ![0-9]+}}
 ; VEC:       [[MIDDLE_BLOCK]]:
@@ -1102,7 +1099,7 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification(ptr %dst) {
 ; VEC-NEXT:    [[CMP_I:%.*]] = icmp slt i32 [[IV_NEXT]], 8
 ; VEC-NEXT:    br i1 [[CMP_I]], label %[[LOOP]], label %[[E_EXIT]], {{!llvm.loop ![0-9]+}}
 ; VEC:       [[E_EXIT]]:
-; VEC-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ [[TMP5]], %[[MIDDLE_BLOCK]] ]
+; VEC-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ 8, %[[MIDDLE_BLOCK]] ]
 ; VEC-NEXT:    ret i32 [[RES]]
 ;
 ; INTERLEAVE-LABEL: define i32 @test_iv_uniform_with_outside_use_scev_simplification(
@@ -1120,7 +1117,6 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification(ptr %dst) {
 ; INTERLEAVE-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i16, ptr [[DST]], i32 [[TMP1]]
 ; INTERLEAVE-NEXT:    store i16 0, ptr [[TMP2]], align 2
 ; INTERLEAVE-NEXT:    store i16 0, ptr [[TMP3]], align 2
-; INTERLEAVE-NEXT:    [[TMP5:%.*]] = add i32 [[STEP_2]], [[TMP1]]
 ; INTERLEAVE-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
 ; INTERLEAVE-NEXT:    [[TMP4:%.*]] = icmp eq i32 [[INDEX_NEXT]], 8
 ; INTERLEAVE-NEXT:    br i1 [[TMP4]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], {{!llvm.loop ![0-9]+}}
@@ -1136,7 +1132,7 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification(ptr %dst) {
 ; INTERLEAVE-NEXT:    [[CMP_I:%.*]] = icmp slt i32 [[IV_NEXT]], 8
 ; INTERLEAVE-NEXT:    br i1 [[CMP_I]], label %[[LOOP]], label %[[E_EXIT]], {{!llvm.loop ![0-9]+}}
 ; INTERLEAVE:       [[E_EXIT]]:
-; INTERLEAVE-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ [[TMP5]], %[[MIDDLE_BLOCK]] ]
+; INTERLEAVE-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ 8, %[[MIDDLE_BLOCK]] ]
 ; INTERLEAVE-NEXT:    ret i32 [[RES]]
 ;
 entry:
@@ -1165,8 +1161,6 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification_2(ptr %dst) {
 ; VEC-NEXT:    [[STEP_2:%.*]] = add nsw i32 [[STEP_1]], 1
 ; VEC-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
 ; VEC:       [[VECTOR_PH]]:
-; VEC-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <2 x i32> poison, i32 [[STEP_2]], i64 0
-; VEC-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <2 x i32> [[BROADCAST_SPLATINSERT]], <2 x i32> poison, <2 x i32> zeroinitializer
 ; VEC-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; VEC:       [[VECTOR_BODY]]:
 ; VEC-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
@@ -1179,7 +1173,7 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification_2(ptr %dst) {
 ; VEC-NEXT:    store i16 0, ptr [[TMP2]], align 2
 ; VEC-NEXT:    store i16 0, ptr [[TMP3]], align 2
 ; VEC-NEXT:    [[TMP4:%.*]] = add <2 x i32> [[VEC_IND]], splat (i32 1)
-; VEC-NEXT:    [[TMP5:%.*]] = add <2 x i32> [[BROADCAST_SPLAT]], [[TMP4]]
+; VEC-NEXT:    [[TMP5:%.*]] = add <2 x i32> splat (i32 1), [[TMP4]]
 ; VEC-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
 ; VEC-NEXT:    [[VEC_IND_NEXT]] = add <2 x i32> [[VEC_IND]], splat (i32 4)
 ; VEC-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[INDEX_NEXT]], 4
@@ -1218,7 +1212,7 @@ define i32 @test_iv_uniform_with_outside_use_scev_simplification_2(ptr %dst) {
 ; INTERLEAVE-NEXT:    store i16 0, ptr [[TMP2]], align 2
 ; INTERLEAVE-NEXT:    store i16 0, ptr [[TMP3]], align 2
 ; INTERLEAVE-NEXT:    [[TMP4:%.*]] = add i32 [[TMP1]], 1
-; INTERLEAVE-NEXT:    [[TMP5:%.*]] = add i32 [[STEP_2]], [[TMP4]]
+; INTERLEAVE-NEXT:    [[TMP5:%.*]] = add i32 1, [[TMP4]]
 ; INTERLEAVE-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
 ; INTERLEAVE-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[INDEX_NEXT]], 4
 ; INTERLEAVE-NEXT:    br i1 [[TMP6]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], {{!llvm.loop ![0-9]+}}
diff --git a/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll b/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
index f8bda1cec035f..62623c708ae0d 100644
--- a/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
+++ b/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
@@ -13,7 +13,7 @@ define void @reuse_lcssa_phi_for_add_rec1(ptr %head) {
 ; CHECK-NEXT:    [[IV_2:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[IV_2_NEXT:%.*]], %[[LOOP_1]] ]
 ; CHECK-NEXT:    [[FOR:%.*]] = phi ptr [ [[HEAD]], %[[ENTRY]] ], [ [[L_1:%.*]], %[[LOOP_1]] ]
 ; CHECK-NEXT:    [[L_1]] = load ptr, ptr [[FOR]], align 8
-; CHECK-NEXT:    [[IV_2_NEXT]] = add nuw nsw i32 [[IV_2]], 1
+; CHECK-NEXT:    [[IV_2_NEXT]] = add nuw i32 [[IV_2]], 1
 ; CHECK-NEXT:    [[EC_1:%.*]] = icmp eq ptr [[L_1]], null
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw i64 [[IV]], 1
 ; CHECK-NEXT:    br i1 [[EC_1]], label %[[PH:.*]], label %[[LOOP_1]]
diff --git a/llvm/test/Transforms/LoopVectorize/scalable-iv-outside-user.ll b/llvm/test/Transforms/LoopVectorize/scalable-iv-outside-user.ll
index cb61fc6e0a046..a188fc89376e3 100644
--- a/llvm/test/Transforms/LoopVectorize/scalable-iv-outside-user.ll
+++ b/llvm/test/Transforms/LoopVectorize/scalable-iv-outside-user.ll
@@ -13,38 +13,22 @@ define i32 @iv_live_out_wide(ptr %dst) {
 ; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    [[TMP4:%.*]] = call i32 @llvm.vscale.i32()
-; CHECK-NEXT:    [[TMP5:%.*]] = mul nuw i32 [[TMP4]], 2
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT1:%.*]] = insertelement <vscale x 2 x i32> poison, i32 [[TMP5]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT2:%.*]] = shufflevector <vscale x 2 x i32> [[BROADCAST_SPLATINSERT1]], <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP6:%.*]] = mul i32 [[TMP5]], 2
+; CHECK-NEXT:    [[TMP6:%.*]] = mul nuw i32 [[TMP4]], 4
 ; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i32 2000, [[TMP6]]
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i32 2000, [[N_MOD_VF]]
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 2 x i32> poison, i32 [[STEP_2]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 2 x i32> [[BROADCAST_SPLATINSERT]], <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP7:%.*]] = call <vscale x 2 x i32> @llvm.stepvector.nxv2i32()
-; CHECK-NEXT:    [[TMP8:%.*]] = mul <vscale x 2 x i32> [[TMP7]], splat (i32 1)
-; CHECK-NEXT:    [[INDUCTION:%.*]] = add <vscale x 2 x i32> zeroinitializer, [[TMP8]]
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <vscale x 2 x i32> [ [[INDUCTION]], %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[STEP_ADD:%.*]] = add <vscale x 2 x i32> [[VEC_IND]], [[BROADCAST_SPLAT2]]
 ; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i16, ptr [[DST]], i32 [[INDEX]]
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i64 @llvm.vscale.i64()
 ; CHECK-NEXT:    [[TMP13:%.*]] = shl nuw i64 [[TMP12]], 1
 ; CHECK-NEXT:    [[TMP14:%.*]] = getelementptr inbounds i16, ptr [[TMP10]], i64 [[TMP13]]
 ; CHECK-NEXT:    store <vscale x 2 x i16> zeroinitializer, ptr [[TMP10]], align 2
 ; CHECK-NEXT:    store <vscale x 2 x i16> zeroinitializer, ptr [[TMP14]], align 2
-; CHECK-NEXT:    [[TMP15:%.*]] = add <vscale x 2 x i32> [[BROADCAST_SPLAT]], [[STEP_ADD]]
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], [[TMP6]]
-; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <vscale x 2 x i32> [[STEP_ADD]], [[BROADCAST_SPLAT2]]
 ; CHECK-NEXT:    [[TMP16:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
 ; CHECK-NEXT:    br i1 [[TMP16]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       [[MIDDLE_BLOCK]]:
-; CHECK-NEXT:    [[TMP17:%.*]] = call i32 @llvm.vscale.i32()
-; CHECK-NEXT:    [[TMP18:%.*]] = mul nuw i32 [[TMP17]], 2
-; CHECK-NEXT:    [[TMP19:%.*]] = sub i32 [[TMP18]], 1
-; CHECK-NEXT:    [[TMP20:%.*]] = extractelement <vscale x 2 x i32> [[TMP15]], i32 [[TMP19]]
 ; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i32 2000, [[N_VEC]]
 ; CHECK-NEXT:    br i1 [[CMP_N]], label %[[E_EXIT:.*]], label %[[SCALAR_PH]]
 ; CHECK:       [[SCALAR_PH]]:
@@ -58,7 +42,7 @@ define i32 @iv_live_out_wide(ptr %dst) {
 ; CHECK-NEXT:    [[CMP_I:%.*]] = icmp slt i32 [[IV_NEXT]], 2000
 ; CHECK-NEXT:    br i1 [[CMP_I]], label %[[LOOP]], label %[[E_EXIT]], !llvm.loop [[LOOP3:![0-9]+]]
 ; CHECK:       [[E_EXIT]]:
-; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ [[TMP20]], %[[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[IV_NEXT]], %[[LOOP]] ], [ [[N_VEC]], %[[MIDDLE_BLOCK]] ]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
 entry:

>From 05b8c93ac2430692258015a7cc9fd8c4a2599104 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Thu, 11 Sep 2025 16:12:24 +0100
Subject: [PATCH 2/2] !fixup adjust naming, use getSCEVExprForVPValue.

---
 .../Vectorize/VPlanConstruction.cpp           | 19 +++++++++----------
 llvm/lib/Transforms/Vectorize/VPlanUtils.cpp  |  3 ++-
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index 72423fee790f7..714ad7fbd33a8 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -532,20 +532,19 @@ static void addInitialSkeleton(VPlan &Plan, Type *InductionTy, DebugLoc IVDL,
   createExtractsForLiveOuts(Plan, MiddleVPBB);
 }
 
-static void simplifyPlanWithSCEV(VPlan &Plan, ScalarEvolution &SE) {
-  auto SimplifyWithSCEV = [&](VPValue *VPV) -> VPValue * {
-    Value *UV = VPV->getUnderlyingValue();
-    if (!UV || !SE.isSCEVable(UV->getType()))
-      return nullptr;
-    auto *S = SE.getSCEV(UV);
-    if (auto *C = dyn_cast<SCEVConstant>(S))
+/// Check \p Plan's live-in and replace them with constants, if they can be
+/// simplified via SCEV.
+static void simplifyLiveInsWithSCEV(VPlan &Plan, ScalarEvolution &SE) {
+  auto GetSimplifiedLiveInViaSCEV = [&](VPValue *VPV) -> VPValue * {
+    const SCEV *Expr = vputils::getSCEVExprForVPValue(VPV, SE);
+    if (auto *C = dyn_cast<SCEVConstant>(Expr))
       return Plan.getOrAddLiveIn(C->getValue());
     return nullptr;
   };
 
   for (VPValue *LiveIn : Plan.getLiveIns()) {
-    if (auto *Simp = SimplifyWithSCEV(LiveIn))
-      LiveIn->replaceAllUsesWith(Simp);
+    if (VPValue *SimplifiedLiveIn = GetSimplifiedLiveInViaSCEV(LiveIn))
+      LiveIn->replaceAllUsesWith(SimplifiedLiveIn);
   }
 }
 
@@ -555,7 +554,7 @@ VPlanTransforms::buildVPlan0(Loop *TheLoop, LoopInfo &LI, Type *InductionTy,
   PlainCFGBuilder Builder(TheLoop, &LI);
   std::unique_ptr<VPlan> VPlan0 = Builder.buildPlainCFG();
   addInitialSkeleton(*VPlan0, InductionTy, IVDL, PSE, TheLoop);
-  simplifyPlanWithSCEV(*VPlan0, *PSE.getSE());
+  simplifyLiveInsWithSCEV(*VPlan0, *PSE.getSE());
   return VPlan0;
 }
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
index c6c1ef3369825..8fb2f533f2bfb 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
@@ -78,7 +78,8 @@ bool vputils::isHeaderMask(const VPValue *V, VPlan &Plan) {
 
 const SCEV *vputils::getSCEVExprForVPValue(VPValue *V, ScalarEvolution &SE) {
   if (V->isLiveIn()) {
-    if (Value *LiveIn = V->getLiveInIRValue())
+    Value *LiveIn = V->getLiveInIRValue();
+    if (LiveIn && SE.isSCEVable(LiveIn->getType()))
       return SE.getSCEV(LiveIn);
     return SE.getCouldNotCompute();
   }



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