[llvm] [VPlan] Migrate replaceSymbolicStride to VPSCEVExpander (PR #208937)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon created https://github.com/llvm/llvm-project/pull/208937

None

>From 9607b2a3184aac95a040fbaadcd64bed6d6f5e1e Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Sat, 11 Jul 2026 20:15:13 +0100
Subject: [PATCH] [VPlan] Migrate replaceSymbolicStride to VPSCEVExpander

---
 llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp    |  7 ++++++-
 .../LoopVectorize/reuse-lcssa-phi-scev-expansion.ll  | 12 ++++++------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index f8198cf9133bf..b4205c3c20844 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -3698,7 +3698,12 @@ void VPlanTransforms::replaceSymbolicStrides(
     auto *NewSCEV =
         SCEVParameterRewriter::rewrite(ScevExpr, *PSE.getSE(), RewriteMap);
     if (NewSCEV != ScevExpr) {
-      VPValue *NewExp = vputils::getOrCreateVPValueForSCEVExpr(Plan, NewSCEV);
+      VPBuilder Builder(Plan.getEntry());
+      VPValue *NewExp =
+          VPSCEVExpander(Builder, *PSE.getSE(), ExpSCEV->getDebugLoc())
+              .tryToExpand(NewSCEV);
+      if (!NewExp)
+        NewExp = VPBuilder(Plan.getEntry()).createExpandSCEV(NewSCEV);
       ExpSCEV->replaceAllUsesWith(NewExp);
       if (Plan.getTripCount() == ExpSCEV)
         Plan.resetTripCount(NewExp);
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 86167582bd12e..ea33b5f6f36ca 100644
--- a/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
+++ b/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
@@ -206,15 +206,10 @@ define void @expand_diff_scev_unknown(ptr %dst, i1 %invar.c, i32 %step) mustprog
 ; CHECK-NEXT:    br i1 [[INVAR_C]], label %[[LOOP_2_PREHEADER:.*]], label %[[LOOP_1]]
 ; CHECK:       [[LOOP_2_PREHEADER]]:
 ; CHECK-NEXT:    [[IV_1_LCSSA:%.*]] = phi i32 [ [[IV_1]], %[[LOOP_1]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = sub i32 2, [[STEP]]
-; CHECK-NEXT:    [[TMP12:%.*]] = add i32 [[IV_1_LCSSA]], [[TMP0]]
-; CHECK-NEXT:    [[SMAX1:%.*]] = call i32 @llvm.smax.i32(i32 [[TMP12]], i32 0)
-; CHECK-NEXT:    [[TMP3:%.*]] = mul i32 [[INDVAR]], -1
-; CHECK-NEXT:    [[TMP14:%.*]] = add i32 [[TMP3]], -1
-; CHECK-NEXT:    [[TMP15:%.*]] = add i32 [[SMAX1]], [[TMP14]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[IV_1_LCSSA]], [[STEP]]
 ; CHECK-NEXT:    [[SMAX:%.*]] = call i32 @llvm.smax.i32(i32 [[TMP1]], i32 0)
 ; CHECK-NEXT:    [[TMP2:%.*]] = mul i32 [[STEP]], -2
+; CHECK-NEXT:    [[TMP3:%.*]] = mul i32 [[INDVAR]], -1
 ; CHECK-NEXT:    [[TMP4:%.*]] = add i32 [[TMP3]], [[TMP2]]
 ; CHECK-NEXT:    [[TMP5:%.*]] = add i32 [[SMAX]], [[TMP4]]
 ; CHECK-NEXT:    [[UMIN:%.*]] = call i32 @llvm.umin.i32(i32 [[TMP5]], i32 1)
@@ -223,6 +218,11 @@ define void @expand_diff_scev_unknown(ptr %dst, i1 %invar.c, i32 %step) mustprog
 ; CHECK-NEXT:    [[UMAX:%.*]] = call i32 @llvm.umax.i32(i32 [[STEP]], i32 1)
 ; CHECK-NEXT:    [[TMP8:%.*]] = udiv i32 [[TMP7]], [[UMAX]]
 ; CHECK-NEXT:    [[TMP9:%.*]] = add i32 [[TMP6]], [[TMP8]]
+; CHECK-NEXT:    [[TMP12:%.*]] = sub i32 2, [[STEP]]
+; CHECK-NEXT:    [[TMP14:%.*]] = add i32 [[IV_1_LCSSA]], [[TMP12]]
+; CHECK-NEXT:    [[SMAX1:%.*]] = call i32 @llvm.smax.i32(i32 [[TMP14]], i32 0)
+; CHECK-NEXT:    [[TMP16:%.*]] = add i32 [[TMP3]], -1
+; CHECK-NEXT:    [[TMP15:%.*]] = add i32 [[SMAX1]], [[TMP16]]
 ; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i32 [[TMP15]], 2
 ; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_SCEVCHECK:.*]]
 ; CHECK:       [[VECTOR_SCEVCHECK]]: