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+//===- SimplifyLibCalls.cpp - Optimize specific well-known library calls --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a simple pass that applies a variety of small
+// optimizations for calls to specific well-known function calls (e.g. runtime
+// library functions). Any optimization that takes the very simple form
+// "replace call to library function with simpler code that provides the same
+// result" belongs in this file.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "simplify-libcalls"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Config/config.h" // FIXME: Shouldn't depend on host!
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetLibraryInfo.h"
+#include "llvm/Transforms/Utils/BuildLibCalls.h"
+using namespace llvm;
+
+
+//===----------------------------------------------------------------------===//
+// Optimizer Base Class
+//===----------------------------------------------------------------------===//
+
+/// This class is the abstract base class for the set of optimizations that
+/// corresponds to one library call.
+namespace {
+class LibCallOptimization {
+protected:
+ Function *Caller;
+ const DataLayout *TD;
+ const TargetLibraryInfo *TLI;
+ LLVMContext* Context;
+public:
+ LibCallOptimization() { }
+ virtual ~LibCallOptimization() {}
+
+ /// CallOptimizer - This pure virtual method is implemented by base classes to
+ /// do various optimizations. If this returns null then no transformation was
+ /// performed. If it returns CI, then it transformed the call and CI is to be
+ /// deleted. If it returns something else, replace CI with the new value and
+ /// delete CI.
+ virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B)
+ =0;
+
+ Value *OptimizeCall(CallInst *CI, const DataLayout *TD,
+ const TargetLibraryInfo *TLI, IRBuilder<> &B) {
+ Caller = CI->getParent()->getParent();
+ this->TD = TD;
+ this->TLI = TLI;
+ if (CI->getCalledFunction())
+ Context = &CI->getCalledFunction()->getContext();
+
+ // We never change the calling convention.
+ if (CI->getCallingConv() != llvm::CallingConv::C)
+ return NULL;
+
+ return CallOptimizer(CI->getCalledFunction(), CI, B);
+ }
+};
+} // End anonymous namespace.
+
+
+//===----------------------------------------------------------------------===//
+// SimplifyLibCalls Pass Implementation
+//===----------------------------------------------------------------------===//
+
+namespace {
+ /// This pass optimizes well known library functions from libc and libm.
+ ///
+ class SimplifyLibCalls : public FunctionPass {
+ TargetLibraryInfo *TLI;
+
+ StringMap<LibCallOptimization*> Optimizations;
+ public:
+ static char ID; // Pass identification
+ SimplifyLibCalls() : FunctionPass(ID) {
+ initializeSimplifyLibCallsPass(*PassRegistry::getPassRegistry());
+ }
+ void AddOpt(LibFunc::Func F, LibCallOptimization* Opt);
+ void AddOpt(LibFunc::Func F1, LibFunc::Func F2, LibCallOptimization* Opt);
+
+ void InitOptimizations();
+ bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<TargetLibraryInfo>();
+ }
+ };
+} // end anonymous namespace.
+
+char SimplifyLibCalls::ID = 0;
+
+INITIALIZE_PASS_BEGIN(SimplifyLibCalls, "simplify-libcalls",
+ "Simplify well-known library calls", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
+INITIALIZE_PASS_END(SimplifyLibCalls, "simplify-libcalls",
+ "Simplify well-known library calls", false, false)
+
+// Public interface to the Simplify LibCalls pass.
+FunctionPass *llvm::createSimplifyLibCallsPass() {
+ return new SimplifyLibCalls();
+}
+
+void SimplifyLibCalls::AddOpt(LibFunc::Func F, LibCallOptimization* Opt) {
+ if (TLI->has(F))
+ Optimizations[TLI->getName(F)] = Opt;
+}
+
+void SimplifyLibCalls::AddOpt(LibFunc::Func F1, LibFunc::Func F2,
+ LibCallOptimization* Opt) {
+ if (TLI->has(F1) && TLI->has(F2))
+ Optimizations[TLI->getName(F1)] = Opt;
+}
+
+/// Optimizations - Populate the Optimizations map with all the optimizations
+/// we know.
+void SimplifyLibCalls::InitOptimizations() {
+}
+
+
+/// runOnFunction - Top level algorithm.
+///
+bool SimplifyLibCalls::runOnFunction(Function &F) {
+ TLI = &getAnalysis<TargetLibraryInfo>();
+
+ if (Optimizations.empty())
+ InitOptimizations();
+
+ const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
+
+ IRBuilder<> Builder(F.getContext());
+
+ bool Changed = false;
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ // Ignore non-calls.
+ CallInst *CI = dyn_cast<CallInst>(I++);
+ if (!CI || CI->hasFnAttr(Attribute::NoBuiltin)) continue;
+
+ // Ignore indirect calls and calls to non-external functions.
+ Function *Callee = CI->getCalledFunction();
+ if (Callee == 0 || !Callee->isDeclaration() ||
+ !(Callee->hasExternalLinkage() || Callee->hasDLLImportLinkage()))
+ continue;
+
+ // Ignore unknown calls.
+ LibCallOptimization *LCO = Optimizations.lookup(Callee->getName());
+ if (!LCO) continue;
+
+ // Set the builder to the instruction after the call.
+ Builder.SetInsertPoint(BB, I);
+
+ // Use debug location of CI for all new instructions.
+ Builder.SetCurrentDebugLocation(CI->getDebugLoc());
+
+ // Try to optimize this call.
+ Value *Result = LCO->OptimizeCall(CI, TD, TLI, Builder);
+ if (Result == 0) continue;
+
+ DEBUG(dbgs() << "SimplifyLibCalls simplified: " << *CI;
+ dbgs() << " into: " << *Result << "\n");
+
+ // Something changed!
+ Changed = true;
+
+ // Inspect the instruction after the call (which was potentially just
+ // added) next.
+ I = CI; ++I;
+
+ if (CI != Result && !CI->use_empty()) {
+ CI->replaceAllUsesWith(Result);
+ if (!Result->hasName())
+ Result->takeName(CI);
+ }
+ CI->eraseFromParent();
+ }
+ }
+ return Changed;
+}
+
+// TODO:
+// Additional cases that we need to add to this file:
+//
+// cbrt:
+// * cbrt(expN(X)) -> expN(x/3)
+// * cbrt(sqrt(x)) -> pow(x,1/6)
+// * cbrt(sqrt(x)) -> pow(x,1/9)
+//
+// exp, expf, expl:
+// * exp(log(x)) -> x
+//
+// log, logf, logl:
+// * log(exp(x)) -> x
+// * log(x**y) -> y*log(x)
+// * log(exp(y)) -> y*log(e)
+// * log(exp2(y)) -> y*log(2)
+// * log(exp10(y)) -> y*log(10)
+// * log(sqrt(x)) -> 0.5*log(x)
+// * log(pow(x,y)) -> y*log(x)
+//
+// lround, lroundf, lroundl:
+// * lround(cnst) -> cnst'
+//
+// pow, powf, powl:
+// * pow(exp(x),y) -> exp(x*y)
+// * pow(sqrt(x),y) -> pow(x,y*0.5)
+// * pow(pow(x,y),z)-> pow(x,y*z)
+//
+// round, roundf, roundl:
+// * round(cnst) -> cnst'
+//
+// signbit:
+// * signbit(cnst) -> cnst'
+// * signbit(nncst) -> 0 (if pstv is a non-negative constant)
+//
+// sqrt, sqrtf, sqrtl:
+// * sqrt(expN(x)) -> expN(x*0.5)
+// * sqrt(Nroot(x)) -> pow(x,1/(2*N))
+// * sqrt(pow(x,y)) -> pow(|x|,y*0.5)
+//
+// strchr:
+// * strchr(p, 0) -> strlen(p)
+// tan, tanf, tanl:
+// * tan(atan(x)) -> x
+//
+// trunc, truncf, truncl:
+// * trunc(cnst) -> cnst'
+//
+//
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