[llvm] 15bf707 - [VPlan] Support truncated IVs in getSCEVExprForVPValue. (NFCI)

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2025-12-25T22:03:29Z
New Revision: 15bf7079b0a99cb6cb77e7600fae0aa4cddb0a57

URL: https://github.com/llvm/llvm-project/commit/15bf7079b0a99cb6cb77e7600fae0aa4cddb0a57
DIFF: https://github.com/llvm/llvm-project/commit/15bf7079b0a99cb6cb77e7600fae0aa4cddb0a57.diff

LOG: [VPlan] Support truncated IVs in getSCEVExprForVPValue. (NFCI)

Handle truncated inductions in getSCEVExprForVPValue. This means we are
able to compute SCEV expressions for more inductions used in the
VPlan-based cost model, which should produce costs matching the legacy
cost model.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/VPlanUtils.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
index dac5ba1b990b8..165eac7d19a56 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
@@ -137,7 +137,11 @@ const SCEV *vputils::getSCEVExprForVPValue(const VPValue *V,
               return SE.getCouldNotCompute();
             const SCEV *Start =
                 getSCEVExprForVPValue(R->getStartValue(), PSE, L);
-            return SE.getAddRecExpr(Start, Step, L, SCEV::FlagAnyWrap);
+            const SCEV *AddRec =
+                SE.getAddRecExpr(Start, Step, L, SCEV::FlagAnyWrap);
+            if (R->getTruncInst())
+              return SE.getTruncateExpr(AddRec, R->getScalarType());
+            return AddRec;
           })
       .Case<VPDerivedIVRecipe>([&SE, &PSE, L](const VPDerivedIVRecipe *R) {
         const SCEV *Start = getSCEVExprForVPValue(R->getOperand(0), PSE, L);