WarnMissedTransforms.cpp

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//===- LoopTransformWarning.cpp -  ----------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Emit warnings if forced code transformations have not been performed.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
 
using namespace llvm;
 
#define DEBUG_TYPE "transform-warning"
 
/// Emit warnings for forced (i.e. user-defined) loop transformations which have
/// still not been performed.
static void warnAboutLeftoverTransformations(Loop *L,
                                             OptimizationRemarkEmitter *ORE) {
  if (hasUnrollTransformation(L) == TM_ForcedByUser) {
    LLVM_DEBUG(dbgs() << "Leftover unroll transformation\n");
 
    // Determine whether this loop originated from the vectorizer so we can
    // produce more informative remarks.
    StringRef LoopKind = getLoopVectorizeKindPrefix(L);
 
    ORE->emit(
        DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
                                          "FailedRequestedUnrolling",
                                          L->getStartLoc(), L->getHeader())
        << LoopKind.str() +
               "loop not unrolled: the optimizer was unable to perform the "
               "requested transformation; the transformation might be disabled "
               "or "
               "specified as part of an unsupported transformation ordering");
  }
 
  if (hasUnrollAndJamTransformation(L) == TM_ForcedByUser) {
    LLVM_DEBUG(dbgs() << "Leftover unroll-and-jam transformation\n");
    ORE->emit(
        DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
                                          "FailedRequestedUnrollAndJamming",
                                          L->getStartLoc(), L->getHeader())
        << "loop not unroll-and-jammed: the optimizer was unable to perform "
           "the requested transformation; the transformation might be disabled "
           "or specified as part of an unsupported transformation ordering");
  }
 
  if (hasVectorizeTransformation(L) == TM_ForcedByUser) {
    LLVM_DEBUG(dbgs() << "Leftover vectorization transformation\n");
    std::optional<ElementCount> VectorizeWidth =
        getOptionalElementCountLoopAttribute(L);
    std::optional<int> InterleaveCount =
        getOptionalIntLoopAttribute(L, "llvm.loop.interleave.count");
 
    if (!VectorizeWidth || VectorizeWidth->isVector())
      ORE->emit(
          DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
                                            "FailedRequestedVectorization",
                                            L->getStartLoc(), L->getHeader())
          << "loop not vectorized: the optimizer was unable to perform the "
             "requested transformation; the transformation might be disabled "
             "or specified as part of an unsupported transformation ordering");
    else if (InterleaveCount.value_or(0) != 1)
      ORE->emit(
          DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
                                            "FailedRequestedInterleaving",
                                            L->getStartLoc(), L->getHeader())
          << "loop not interleaved: the optimizer was unable to perform the "
             "requested transformation; the transformation might be disabled "
             "or specified as part of an unsupported transformation ordering");
  }
 
  if (hasDistributeTransformation(L) == TM_ForcedByUser) {
    LLVM_DEBUG(dbgs() << "Leftover distribute transformation\n");
    ORE->emit(
        DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
                                          "FailedRequestedDistribution",
                                          L->getStartLoc(), L->getHeader())
        << "loop not distributed: the optimizer was unable to perform the "
           "requested transformation; the transformation might be disabled or "
           "specified as part of an unsupported transformation ordering");
  }
}
 
static void warnAboutLeftoverTransformations(Function *F, LoopInfo *LI,
                                             OptimizationRemarkEmitter *ORE) {
  for (auto *L : LI->getLoopsInPreorder())
    warnAboutLeftoverTransformations(L, ORE);
}
 
// New pass manager boilerplate
PreservedAnalyses
WarnMissedTransformationsPass::run(Function &F, FunctionAnalysisManager &AM) {
  // Do not warn about not applied transformations if optimizations are
  // disabled.
  if (F.hasOptNone())
    return PreservedAnalyses::all();
 
  auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
  auto &LI = AM.getResult<LoopAnalysis>(F);
 
  warnAboutLeftoverTransformations(&F, &LI, &ORE);
 
  return PreservedAnalyses::all();
}