[llvm] 75d0e0c - [IRCE] consolidate profitability check

[Serguei Katkov via llvm-commits]

Author: Serguei Katkov
Date: 2020-10-22T11:26:45+07:00
New Revision: 75d0e0cd5f4c584f235b98e13c01421683bf0b80

URL: https://github.com/llvm/llvm-project/commit/75d0e0cd5f4c584f235b98e13c01421683bf0b80
DIFF: https://github.com/llvm/llvm-project/commit/75d0e0cd5f4c584f235b98e13c01421683bf0b80.diff

LOG: [IRCE] consolidate profitability check

Use BFI if it is available and BPI otherwise.
This is a promised follow-up after D89541.

Reviewers: ebrevnov, mkazantsev
Reviewed By: ebrevnov
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D89773

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index be7527b3efd1..ef5ea30ffeac 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -233,6 +233,8 @@ class InductiveRangeCheck {
                                SmallVectorImpl<InductiveRangeCheck> &Checks);
 };
 
+struct LoopStructure;
+
 class InductiveRangeCheckElimination {
   ScalarEvolution &SE;
   BranchProbabilityInfo *BPI;
@@ -243,6 +245,10 @@ class InductiveRangeCheckElimination {
       llvm::Optional<llvm::function_ref<llvm::BlockFrequencyInfo &()> >;
   GetBFIFunc GetBFI;
 
+  // Returns true if it is profitable to do a transform basing on estimation of
+  // number of iterations.
+  bool isProfitableToTransform(const Loop &L, LoopStructure &LS);
+
 public:
   InductiveRangeCheckElimination(ScalarEvolution &SE,
                                  BranchProbabilityInfo *BPI, DominatorTree &DT,
@@ -505,9 +511,8 @@ struct LoopStructure {
     return Result;
   }
 
-  static Optional<LoopStructure> parseLoopStructure(ScalarEvolution &,
-                                                    BranchProbabilityInfo *BPI,
-                                                    Loop &, const char *&);
+  static Optional<LoopStructure> parseLoopStructure(ScalarEvolution &, Loop &,
+                                                    const char *&);
 };
 
 /// This class is used to constrain loops to run within a given iteration space.
@@ -751,8 +756,7 @@ static bool isSafeIncreasingBound(const SCEV *Start,
 }
 
 Optional<LoopStructure>
-LoopStructure::parseLoopStructure(ScalarEvolution &SE,
-                                  BranchProbabilityInfo *BPI, Loop &L,
+LoopStructure::parseLoopStructure(ScalarEvolution &SE, Loop &L,
                                   const char *&FailureReason) {
   if (!L.isLoopSimplifyForm()) {
     FailureReason = "loop not in LoopSimplify form";
@@ -787,16 +791,6 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
 
   unsigned LatchBrExitIdx = LatchBr->getSuccessor(0) == Header ? 1 : 0;
 
-  BranchProbability ExitProbability =
-      BPI ? BPI->getEdgeProbability(LatchBr->getParent(), LatchBrExitIdx)
-          : BranchProbability::getZero();
-
-  if (!SkipProfitabilityChecks &&
-      ExitProbability > BranchProbability(1, MaxExitProbReciprocal)) {
-    FailureReason = "short running loop, not profitable";
-    return None;
-  }
-
   ICmpInst *ICI = dyn_cast<ICmpInst>(LatchBr->getCondition());
   if (!ICI || !isa<IntegerType>(ICI->getOperand(0)->getType())) {
     FailureReason = "latch terminator branch not conditional on integral icmp";
@@ -1855,6 +1849,37 @@ bool IRCELegacyPass::runOnFunction(Function &F) {
   return Changed;
 }
 
+bool
+InductiveRangeCheckElimination::isProfitableToTransform(const Loop &L,
+                                                        LoopStructure &LS) {
+  if (SkipProfitabilityChecks)
+    return true;
+  if (GetBFI.hasValue()) {
+    BlockFrequencyInfo &BFI = (*GetBFI)();
+    uint64_t hFreq = BFI.getBlockFreq(LS.Header).getFrequency();
+    uint64_t phFreq = BFI.getBlockFreq(L.getLoopPreheader()).getFrequency();
+    if (phFreq != 0 && hFreq != 0 && (hFreq / phFreq < MinRuntimeIterations)) {
+      LLVM_DEBUG(dbgs() << "irce: could not prove profitability: "
+                        << "the estimated number of iterations basing on "
+                           "frequency info is " << (hFreq / phFreq) << "\n";);
+      return false;
+    }
+    return true;
+  }
+
+  if (!BPI)
+    return true;
+  BranchProbability ExitProbability =
+      BPI->getEdgeProbability(LS.Latch, LS.LatchBrExitIdx);
+  if (ExitProbability > BranchProbability(1, MaxExitProbReciprocal)) {
+    LLVM_DEBUG(dbgs() << "irce: could not prove profitability: "
+                      << "the exit probability is too big " << ExitProbability
+                      << "\n";);
+    return false;
+  }
+  return true;
+}
+
 bool InductiveRangeCheckElimination::run(
     Loop *L, function_ref<void(Loop *, bool)> LPMAddNewLoop) {
   if (L->getBlocks().size() >= LoopSizeCutoff) {
@@ -1894,25 +1919,15 @@ bool InductiveRangeCheckElimination::run(
 
   const char *FailureReason = nullptr;
   Optional<LoopStructure> MaybeLoopStructure =
-      LoopStructure::parseLoopStructure(SE, BPI, *L, FailureReason);
+      LoopStructure::parseLoopStructure(SE, *L, FailureReason);
   if (!MaybeLoopStructure.hasValue()) {
     LLVM_DEBUG(dbgs() << "irce: could not parse loop structure: "
                       << FailureReason << "\n";);
     return false;
   }
   LoopStructure LS = MaybeLoopStructure.getValue();
-  // Profitability check.
-  if (!SkipProfitabilityChecks && GetBFI.hasValue()) {
-    BlockFrequencyInfo &BFI = (*GetBFI)();
-    uint64_t hFreq = BFI.getBlockFreq(LS.Header).getFrequency();
-    uint64_t phFreq = BFI.getBlockFreq(Preheader).getFrequency();
-    if (phFreq != 0 && hFreq != 0 && (hFreq / phFreq < MinRuntimeIterations)) {
-      LLVM_DEBUG(dbgs() << "irce: could not prove profitability: "
-                        << "the estimated number of iterations basing on "
-                           "frequency info is " << (hFreq / phFreq) << "\n";);
-      return false;
-    }
-  }
+  if (!isProfitableToTransform(*L, LS))
+    return false;
   const SCEVAddRecExpr *IndVar =
       cast<SCEVAddRecExpr>(SE.getMinusSCEV(SE.getSCEV(LS.IndVarBase), SE.getSCEV(LS.IndVarStep)));