llvm/llvm/lib/Transforms/Utils/LibCallsShrinkWrap.cpp

//===-- LibCallsShrinkWrap.cpp ----------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This pass shrink-wraps a call to function if the result is not used.
// The call can set errno but is otherwise side effect free. For example:
//    sqrt(val);
//  is transformed to
//    if (val < 0)
//      sqrt(val);
//  Even if the result of library call is not being used, the compiler cannot
//  safely delete the call because the function can set errno on error
//  conditions.
//  Note in many functions, the error condition solely depends on the incoming
//  parameter. In this optimization, we can generate the condition can lead to
//  the errno to shrink-wrap the call. Since the chances of hitting the error
//  condition is low, the runtime call is effectively eliminated.
//
//  These partially dead calls are usually results of C++ abstraction penalty
//  exposed by inlining.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/LibCallsShrinkWrap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"

#include <cmath>

usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumWrappedOneCond, "Number of One-Condition Wrappers Inserted");
STATISTIC(NumWrappedTwoCond, "Number of Two-Condition Wrappers Inserted");

namespace {
class LibCallsShrinkWrap : public InstVisitor<LibCallsShrinkWrap> { … };
} // end anonymous namespace

// Perform the transformation to calls with errno set by domain error.
bool LibCallsShrinkWrap::performCallDomainErrorOnly(CallInst *CI,
                                                    const LibFunc &Func) { … }

// Perform the transformation to calls with errno set by range error.
bool LibCallsShrinkWrap::performCallRangeErrorOnly(CallInst *CI,
                                                   const LibFunc &Func) { … }

// Perform the transformation to calls with errno set by combination of errors.
bool LibCallsShrinkWrap::performCallErrors(CallInst *CI,
                                           const LibFunc &Func) { … }

// Checks if CI is a candidate for shrinkwrapping and put it into work list if
// true.
void LibCallsShrinkWrap::checkCandidate(CallInst &CI) { … }

// Generate the upper bound condition for RangeError.
Value *LibCallsShrinkWrap::generateOneRangeCond(CallInst *CI,
                                                const LibFunc &Func) { … }

// Generate the lower and upper bound condition for RangeError.
Value *LibCallsShrinkWrap::generateTwoRangeCond(CallInst *CI,
                                                const LibFunc &Func) { … }

// For pow(x,y), We only handle the following cases:
// (1) x is a constant && (x >= 1) && (x < MaxUInt8)
//     Cond is: (y > 127)
// (2) x is a value coming from an integer type.
//   (2.1) if x's bit_size == 8
//         Cond: (x <= 0 || y > 128)
//   (2.2) if x's bit_size is 16
//         Cond: (x <= 0 || y > 64)
//   (2.3) if x's bit_size is 32
//         Cond: (x <= 0 || y > 32)
// Support for powl(x,y) and powf(x,y) are TBD.
//
// Note that condition can be more conservative than the actual condition
// (i.e. we might invoke the calls that will not set the errno.).
//
Value *LibCallsShrinkWrap::generateCondForPow(CallInst *CI,
                                              const LibFunc &Func) { … }

// Wrap conditions that can potentially generate errno to the library call.
void LibCallsShrinkWrap::shrinkWrapCI(CallInst *CI, Value *Cond) { … }

// Perform the transformation to a single candidate.
bool LibCallsShrinkWrap::perform(CallInst *CI) { … }

static bool runImpl(Function &F, const TargetLibraryInfo &TLI,
                    DominatorTree *DT) { … }

PreservedAnalyses LibCallsShrinkWrapPass::run(Function &F,
                                              FunctionAnalysisManager &FAM) { … }