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llvm-project/llvm/lib/Transforms/Utils/LibCallsShrinkWrap.cpp
Davide Italiano 1e77aaca8a [LibcallsShrinkWrap] This pass doesn't preserve the CFG. 
For example, it invalidates the domtree, causing assertions
in later passes which need dominator infos. Make it preserve
GlobalsAA, as suggested by Eli.

Differential Revision:  https://reviews.llvm.org/D26381

llvm-svn: 286271
2016-11-08 19:18:20 +00:00

570 lines
19 KiB
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//===-- LibCallsShrinkWrap.cpp ----------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/GlobalsModRef.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
#define DEBUG_TYPE "libcalls-shrinkwrap"
STATISTIC(NumWrappedOneCond, "Number of One-Condition Wrappers Inserted");
STATISTIC(NumWrappedTwoCond, "Number of Two-Condition Wrappers Inserted");
static cl::opt<bool> LibCallsShrinkWrapDoDomainError(
"libcalls-shrinkwrap-domain-error", cl::init(true), cl::Hidden,
cl::desc("Perform shrink-wrap on lib calls with domain errors"));
static cl::opt<bool> LibCallsShrinkWrapDoRangeError(
"libcalls-shrinkwrap-range-error", cl::init(true), cl::Hidden,
cl::desc("Perform shrink-wrap on lib calls with range errors"));
static cl::opt<bool> LibCallsShrinkWrapDoPoleError(
"libcalls-shrinkwrap-pole-error", cl::init(true), cl::Hidden,
cl::desc("Perform shrink-wrap on lib calls with pole errors"));
namespace {
class LibCallsShrinkWrapLegacyPass : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
explicit LibCallsShrinkWrapLegacyPass() : FunctionPass(ID) {
initializeLibCallsShrinkWrapLegacyPassPass(
*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override;
bool runOnFunction(Function &F) override;
};
}
char LibCallsShrinkWrapLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LibCallsShrinkWrapLegacyPass, "libcalls-shrinkwrap",
"Conditionally eliminate dead library calls", false,
false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(LibCallsShrinkWrapLegacyPass, "libcalls-shrinkwrap",
"Conditionally eliminate dead library calls", false, false)
class LibCallsShrinkWrap : public InstVisitor<LibCallsShrinkWrap> {
public:
LibCallsShrinkWrap(const TargetLibraryInfo &TLI) : TLI(TLI), Changed(false){};
bool isChanged() const { return Changed; }
void visitCallInst(CallInst &CI) { checkCandidate(CI); }
void perform() {
for (auto &CI : WorkList) {
DEBUG(dbgs() << "CDCE calls: " << CI->getCalledFunction()->getName()
<< "\n");
if (perform(CI)) {
Changed = true;
DEBUG(dbgs() << "Transformed\n");
}
}
}
private:
bool perform(CallInst *CI);
void checkCandidate(CallInst &CI);
void shrinkWrapCI(CallInst *CI, Value *Cond);
bool performCallDomainErrorOnly(CallInst *CI, const LibFunc::Func &Func);
bool performCallErrors(CallInst *CI, const LibFunc::Func &Func);
bool performCallRangeErrorOnly(CallInst *CI, const LibFunc::Func &Func);
Value *generateOneRangeCond(CallInst *CI, const LibFunc::Func &Func);
Value *generateTwoRangeCond(CallInst *CI, const LibFunc::Func &Func);
Value *generateCondForPow(CallInst *CI, const LibFunc::Func &Func);
// Create an OR of two conditions.
Value *createOrCond(CallInst *CI, CmpInst::Predicate Cmp, float Val,
CmpInst::Predicate Cmp2, float Val2) {
IRBuilder<> BBBuilder(CI);
Value *Arg = CI->getArgOperand(0);
auto Cond2 = createCond(BBBuilder, Arg, Cmp2, Val2);
auto Cond1 = createCond(BBBuilder, Arg, Cmp, Val);
return BBBuilder.CreateOr(Cond1, Cond2);
}
// Create a single condition using IRBuilder.
Value *createCond(IRBuilder<> &BBBuilder, Value *Arg, CmpInst::Predicate Cmp,
float Val) {
Constant *V = ConstantFP::get(BBBuilder.getContext(), APFloat(Val));
if (!Arg->getType()->isFloatTy())
V = ConstantExpr::getFPExtend(V, Arg->getType());
return BBBuilder.CreateFCmp(Cmp, Arg, V);
}
// Create a single condition.
Value *createCond(CallInst *CI, CmpInst::Predicate Cmp, float Val) {
IRBuilder<> BBBuilder(CI);
Value *Arg = CI->getArgOperand(0);
return createCond(BBBuilder, Arg, Cmp, Val);
}
const TargetLibraryInfo &TLI;
SmallVector<CallInst *, 16> WorkList;
bool Changed;
};
// Perform the transformation to calls with errno set by domain error.
bool LibCallsShrinkWrap::performCallDomainErrorOnly(CallInst *CI,
const LibFunc::Func &Func) {
Value *Cond = nullptr;
switch (Func) {
case LibFunc::acos: // DomainError: (x < -1 || x > 1)
case LibFunc::acosf: // Same as acos
case LibFunc::acosl: // Same as acos
case LibFunc::asin: // DomainError: (x < -1 || x > 1)
case LibFunc::asinf: // Same as asin
case LibFunc::asinl: // Same as asin
{
++NumWrappedTwoCond;
Cond = createOrCond(CI, CmpInst::FCMP_OLT, -1.0f, CmpInst::FCMP_OGT, 1.0f);
break;
}
case LibFunc::cos: // DomainError: (x == +inf || x == -inf)
case LibFunc::cosf: // Same as cos
case LibFunc::cosl: // Same as cos
case LibFunc::sin: // DomainError: (x == +inf || x == -inf)
case LibFunc::sinf: // Same as sin
case LibFunc::sinl: // Same as sin
{
++NumWrappedTwoCond;
Cond = createOrCond(CI, CmpInst::FCMP_OEQ, INFINITY, CmpInst::FCMP_OEQ,
-INFINITY);
break;
}
case LibFunc::acosh: // DomainError: (x < 1)
case LibFunc::acoshf: // Same as acosh
case LibFunc::acoshl: // Same as acosh
{
++NumWrappedOneCond;
Cond = createCond(CI, CmpInst::FCMP_OLT, 1.0f);
break;
}
case LibFunc::sqrt: // DomainError: (x < 0)
case LibFunc::sqrtf: // Same as sqrt
case LibFunc::sqrtl: // Same as sqrt
{
++NumWrappedOneCond;
Cond = createCond(CI, CmpInst::FCMP_OLT, 0.0f);
break;
}
default:
return false;
}
shrinkWrapCI(CI, Cond);
return true;
}
// Perform the transformation to calls with errno set by range error.
bool LibCallsShrinkWrap::performCallRangeErrorOnly(CallInst *CI,
const LibFunc::Func &Func) {
Value *Cond = nullptr;
switch (Func) {
case LibFunc::cosh:
case LibFunc::coshf:
case LibFunc::coshl:
case LibFunc::exp:
case LibFunc::expf:
case LibFunc::expl:
case LibFunc::exp10:
case LibFunc::exp10f:
case LibFunc::exp10l:
case LibFunc::exp2:
case LibFunc::exp2f:
case LibFunc::exp2l:
case LibFunc::sinh:
case LibFunc::sinhf:
case LibFunc::sinhl: {
Cond = generateTwoRangeCond(CI, Func);
break;
}
case LibFunc::expm1: // RangeError: (709, inf)
case LibFunc::expm1f: // RangeError: (88, inf)
case LibFunc::expm1l: // RangeError: (11356, inf)
{
Cond = generateOneRangeCond(CI, Func);
break;
}
default:
return false;
}
shrinkWrapCI(CI, Cond);
return true;
}
// Perform the transformation to calls with errno set by combination of errors.
bool LibCallsShrinkWrap::performCallErrors(CallInst *CI,
const LibFunc::Func &Func) {
Value *Cond = nullptr;
switch (Func) {
case LibFunc::atanh: // DomainError: (x < -1 || x > 1)
// PoleError: (x == -1 || x == 1)
// Overall Cond: (x <= -1 || x >= 1)
case LibFunc::atanhf: // Same as atanh
case LibFunc::atanhl: // Same as atanh
{
if (!LibCallsShrinkWrapDoDomainError || !LibCallsShrinkWrapDoPoleError)
return false;
++NumWrappedTwoCond;
Cond = createOrCond(CI, CmpInst::FCMP_OLE, -1.0f, CmpInst::FCMP_OGE, 1.0f);
break;
}
case LibFunc::log: // DomainError: (x < 0)
// PoleError: (x == 0)
// Overall Cond: (x <= 0)
case LibFunc::logf: // Same as log
case LibFunc::logl: // Same as log
case LibFunc::log10: // Same as log
case LibFunc::log10f: // Same as log
case LibFunc::log10l: // Same as log
case LibFunc::log2: // Same as log
case LibFunc::log2f: // Same as log
case LibFunc::log2l: // Same as log
case LibFunc::logb: // Same as log
case LibFunc::logbf: // Same as log
case LibFunc::logbl: // Same as log
{
if (!LibCallsShrinkWrapDoDomainError || !LibCallsShrinkWrapDoPoleError)
return false;
++NumWrappedOneCond;
Cond = createCond(CI, CmpInst::FCMP_OLE, 0.0f);
break;
}
case LibFunc::log1p: // DomainError: (x < -1)
// PoleError: (x == -1)
// Overall Cond: (x <= -1)
case LibFunc::log1pf: // Same as log1p
case LibFunc::log1pl: // Same as log1p
{
if (!LibCallsShrinkWrapDoDomainError || !LibCallsShrinkWrapDoPoleError)
return false;
++NumWrappedOneCond;
Cond = createCond(CI, CmpInst::FCMP_OLE, -1.0f);
break;
}
case LibFunc::pow: // DomainError: x < 0 and y is noninteger
// PoleError: x == 0 and y < 0
// RangeError: overflow or underflow
case LibFunc::powf:
case LibFunc::powl: {
if (!LibCallsShrinkWrapDoDomainError || !LibCallsShrinkWrapDoPoleError ||
!LibCallsShrinkWrapDoRangeError)
return false;
Cond = generateCondForPow(CI, Func);
if (Cond == nullptr)
return false;
break;
}
default:
return false;
}
assert(Cond && "performCallErrors should not see an empty condition");
shrinkWrapCI(CI, Cond);
return true;
}
// Checks if CI is a candidate for shrinkwrapping and put it into work list if
// true.
void LibCallsShrinkWrap::checkCandidate(CallInst &CI) {
if (CI.isNoBuiltin())
return;
// A possible improvement is to handle the calls with the return value being
// used. If there is API for fast libcall implementation without setting
// errno, we can use the same framework to direct/wrap the call to the fast
// API in the error free path, and leave the original call in the slow path.
if (!CI.use_empty())
return;
LibFunc::Func Func;
Function *Callee = CI.getCalledFunction();
if (!Callee)
return;
if (!TLI.getLibFunc(*Callee, Func) || !TLI.has(Func))
return;
if (CI.getNumArgOperands() == 0)
return;
// TODO: Handle long double in other formats.
Type *ArgType = CI.getArgOperand(0)->getType();
if (!(ArgType->isFloatTy() || ArgType->isDoubleTy() ||
ArgType->isX86_FP80Ty()))
return;
WorkList.push_back(&CI);
}
// Generate the upper bound condition for RangeError.
Value *LibCallsShrinkWrap::generateOneRangeCond(CallInst *CI,
const LibFunc::Func &Func) {
float UpperBound;
switch (Func) {
case LibFunc::expm1: // RangeError: (709, inf)
UpperBound = 709.0f;
break;
case LibFunc::expm1f: // RangeError: (88, inf)
UpperBound = 88.0f;
break;
case LibFunc::expm1l: // RangeError: (11356, inf)
UpperBound = 11356.0f;
break;
default:
llvm_unreachable("Should be reach here");
}
++NumWrappedOneCond;
return createCond(CI, CmpInst::FCMP_OGT, UpperBound);
}
// Generate the lower and upper bound condition for RangeError.
Value *LibCallsShrinkWrap::generateTwoRangeCond(CallInst *CI,
const LibFunc::Func &Func) {
float UpperBound, LowerBound;
switch (Func) {
case LibFunc::cosh: // RangeError: (x < -710 || x > 710)
case LibFunc::sinh: // Same as cosh
LowerBound = -710.0f;
UpperBound = 710.0f;
break;
case LibFunc::coshf: // RangeError: (x < -89 || x > 89)
case LibFunc::sinhf: // Same as coshf
LowerBound = -89.0f;
UpperBound = 89.0f;
break;
case LibFunc::coshl: // RangeError: (x < -11357 || x > 11357)
case LibFunc::sinhl: // Same as coshl
LowerBound = -11357.0f;
UpperBound = 11357.0f;
break;
case LibFunc::exp: // RangeError: (x < -745 || x > 709)
LowerBound = -745.0f;
UpperBound = 709.0f;
break;
case LibFunc::expf: // RangeError: (x < -103 || x > 88)
LowerBound = -103.0f;
UpperBound = 88.0f;
break;
case LibFunc::expl: // RangeError: (x < -11399 || x > 11356)
LowerBound = -11399.0f;
UpperBound = 11356.0f;
break;
case LibFunc::exp10: // RangeError: (x < -323 || x > 308)
LowerBound = -323.0f;
UpperBound = 308.0f;
break;
case LibFunc::exp10f: // RangeError: (x < -45 || x > 38)
LowerBound = -45.0f;
UpperBound = 38.0f;
break;
case LibFunc::exp10l: // RangeError: (x < -4950 || x > 4932)
LowerBound = -4950.0f;
UpperBound = 4932.0f;
break;
case LibFunc::exp2: // RangeError: (x < -1074 || x > 1023)
LowerBound = -1074.0f;
UpperBound = 1023.0f;
break;
case LibFunc::exp2f: // RangeError: (x < -149 || x > 127)
LowerBound = -149.0f;
UpperBound = 127.0f;
break;
case LibFunc::exp2l: // RangeError: (x < -16445 || x > 11383)
LowerBound = -16445.0f;
UpperBound = 11383.0f;
break;
default:
llvm_unreachable("Should be reach here");
}
++NumWrappedTwoCond;
return createOrCond(CI, CmpInst::FCMP_OGT, UpperBound, CmpInst::FCMP_OLT,
LowerBound);
}
// 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 &Func) {
// FIXME: LibFunc::powf and powl TBD.
if (Func != LibFunc::pow) {
DEBUG(dbgs() << "Not handled powf() and powl()\n");
return nullptr;
}
Value *Base = CI->getArgOperand(0);
Value *Exp = CI->getArgOperand(1);
IRBuilder<> BBBuilder(CI);
// Constant Base case.
if (ConstantFP *CF = dyn_cast<ConstantFP>(Base)) {
double D = CF->getValueAPF().convertToDouble();
if (D < 1.0f || D > APInt::getMaxValue(8).getZExtValue()) {
DEBUG(dbgs() << "Not handled pow(): constant base out of range\n");
return nullptr;
}
++NumWrappedOneCond;
Constant *V = ConstantFP::get(CI->getContext(), APFloat(127.0f));
if (!Exp->getType()->isFloatTy())
V = ConstantExpr::getFPExtend(V, Exp->getType());
return BBBuilder.CreateFCmp(CmpInst::FCMP_OGT, Exp, V);
}
// If the Base value coming from an integer type.
Instruction *I = dyn_cast<Instruction>(Base);
if (!I) {
DEBUG(dbgs() << "Not handled pow(): FP type base\n");
return nullptr;
}
unsigned Opcode = I->getOpcode();
if (Opcode == Instruction::UIToFP || Opcode == Instruction::SIToFP) {
unsigned BW = I->getOperand(0)->getType()->getPrimitiveSizeInBits();
float UpperV = 0.0f;
if (BW == 8)
UpperV = 128.0f;
else if (BW == 16)
UpperV = 64.0f;
else if (BW == 32)
UpperV = 32.0f;
else {
DEBUG(dbgs() << "Not handled pow(): type too wide\n");
return nullptr;
}
++NumWrappedTwoCond;
Constant *V = ConstantFP::get(CI->getContext(), APFloat(UpperV));
Constant *V0 = ConstantFP::get(CI->getContext(), APFloat(0.0f));
if (!Exp->getType()->isFloatTy())
V = ConstantExpr::getFPExtend(V, Exp->getType());
if (!Base->getType()->isFloatTy())
V0 = ConstantExpr::getFPExtend(V0, Exp->getType());
Value *Cond = BBBuilder.CreateFCmp(CmpInst::FCMP_OGT, Exp, V);
Value *Cond0 = BBBuilder.CreateFCmp(CmpInst::FCMP_OLE, Base, V0);
return BBBuilder.CreateOr(Cond0, Cond);
}
DEBUG(dbgs() << "Not handled pow(): base not from integer convert\n");
return nullptr;
}
// Wrap conditions that can potentially generate errno to the library call.
void LibCallsShrinkWrap::shrinkWrapCI(CallInst *CI, Value *Cond) {
assert(Cond != nullptr && "hrinkWrapCI is not expecting an empty call inst");
MDNode *BranchWeights =
MDBuilder(CI->getContext()).createBranchWeights(1, 2000);
TerminatorInst *NewInst =
SplitBlockAndInsertIfThen(Cond, CI, false, BranchWeights);
BasicBlock *CallBB = NewInst->getParent();
CallBB->setName("cdce.call");
CallBB->getSingleSuccessor()->setName("cdce.end");
CI->removeFromParent();
CallBB->getInstList().insert(CallBB->getFirstInsertionPt(), CI);
DEBUG(dbgs() << "== Basic Block After ==");
DEBUG(dbgs() << *CallBB->getSinglePredecessor() << *CallBB
<< *CallBB->getSingleSuccessor() << "\n");
}
// Perform the transformation to a single candidate.
bool LibCallsShrinkWrap::perform(CallInst *CI) {
LibFunc::Func Func;
Function *Callee = CI->getCalledFunction();
assert(Callee && "perform() should apply to a non-empty callee");
TLI.getLibFunc(*Callee, Func);
assert(Func && "perform() is not expecting an empty function");
if (LibCallsShrinkWrapDoDomainError && performCallDomainErrorOnly(CI, Func))
return true;
if (LibCallsShrinkWrapDoRangeError && performCallRangeErrorOnly(CI, Func))
return true;
return performCallErrors(CI, Func);
}
void LibCallsShrinkWrapLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
bool runImpl(Function &F, const TargetLibraryInfo &TLI) {
if (F.hasFnAttribute(Attribute::OptimizeForSize))
return false;
LibCallsShrinkWrap CCDCE(TLI);
CCDCE.visit(F);
CCDCE.perform();
return CCDCE.isChanged();
}
bool LibCallsShrinkWrapLegacyPass::runOnFunction(Function &F) {
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
return runImpl(F, TLI);
}
namespace llvm {
char &LibCallsShrinkWrapPassID = LibCallsShrinkWrapLegacyPass::ID;
// Public interface to LibCallsShrinkWrap pass.
FunctionPass *createLibCallsShrinkWrapPass() {
return new LibCallsShrinkWrapLegacyPass();
}
PreservedAnalyses LibCallsShrinkWrapPass::run(Function &F,
FunctionAnalysisManager &FAM) {
auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F);
bool Changed = runImpl(F, TLI);
if (!Changed)
return PreservedAnalyses::all();
auto PA = PreservedAnalyses();
PA.preserve<GlobalsAA>();
return PA;
}
}
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