[llvm] [LV][NFCI]Use integer for cost/trip count calculations instead of double, fix possible UB. (PR #87241)

[Alexey Bataev via llvm-commits]

https://github.com/alexey-bataev updated https://github.com/llvm/llvm-project/pull/87241

>From acffe10299160884f93c88d2be6e41638169738b Mon Sep 17 00:00:00 2001
From: Alexey Bataev <a.bataev at outlook.com>
Date: Mon, 1 Apr 2024 14:23:03 +0000
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.5
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 0834865173b2f1..0d391ff1dbe231 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -9584,7 +9584,7 @@ static bool areRuntimeChecksProfitable(GeneratedRTChecks &Checks,
   }
 
   // The scalar cost should only be 0 when vectorizing with a user specified VF/IC. In those cases, runtime checks should always be generated.
-  double ScalarC = *VF.ScalarCost.getValue();
+  uint64_t ScalarC = *VF.ScalarCost.getValue();
   if (ScalarC == 0)
     return true;
 
@@ -9611,7 +9611,7 @@ static bool areRuntimeChecksProfitable(GeneratedRTChecks &Checks,
   //   RtC + VecC * (TC / VF) + EpiC <  ScalarC * TC
   //
   // Now we can compute the minimum required trip count TC as
-  //   (RtC + EpiC) / (ScalarC - (VecC / VF)) < TC
+  //   VF * (RtC + EpiC) / (ScalarC * VF - VecC) < TC
   //
   // For now we assume the epilogue cost EpiC = 0 for simplicity. Note that
   // the computations are performed on doubles, not integers and the result
@@ -9623,9 +9623,9 @@ static bool areRuntimeChecksProfitable(GeneratedRTChecks &Checks,
       AssumedMinimumVscale = *VScale;
     IntVF *= AssumedMinimumVscale;
   }
-  double VecCOverVF = double(*VF.Cost.getValue()) / IntVF;
-  double RtC = *CheckCost.getValue();
-  double MinTC1 = RtC / (ScalarC - VecCOverVF);
+  uint64_t RtC = *CheckCost.getValue();
+  uint64_t Div = ScalarC * IntVF - *VF.Cost.getValue();
+  uint64_t MinTC1 = Div == 0 ? 0 : divideCeil(RtC * IntVF, Div);
 
   // Second, compute a minimum iteration count so that the cost of the
   // runtime checks is only a fraction of the total scalar loop cost. This
@@ -9634,12 +9634,12 @@ static bool areRuntimeChecksProfitable(GeneratedRTChecks &Checks,
   // * TC. To bound the runtime check to be a fraction 1/X of the scalar
   // cost, compute
   //   RtC < ScalarC * TC * (1 / X)  ==>  RtC * X / ScalarC < TC
-  double MinTC2 = RtC * 10 / ScalarC;
+  uint64_t MinTC2 = divideCeil(RtC * 10, ScalarC);
 
   // Now pick the larger minimum. If it is not a multiple of VF and a scalar
   // epilogue is allowed, choose the next closest multiple of VF. This should
   // partly compensate for ignoring the epilogue cost.
-  uint64_t MinTC = std::ceil(std::max(MinTC1, MinTC2));
+  uint64_t MinTC = std::max(MinTC1, MinTC2);
   if (SEL == CM_ScalarEpilogueAllowed)
     MinTC = alignTo(MinTC, IntVF);
   VF.MinProfitableTripCount = ElementCount::getFixed(MinTC);