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//===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
//
// 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 custom inliner that handles only functions that
// are marked as "always inline".
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "inline"
#include "llvm/CallingConv.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Type.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/InlinerPass.h"
#include "llvm/DataLayout.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace llvm;
namespace {
// AlwaysInliner only inlines functions that are mark as "always inline".
class AlwaysInliner : public Inliner {
public:
// Use extremely low threshold.
AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/true) {
initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
}
AlwaysInliner(bool InsertLifetime) : Inliner(ID, -2000000000,
InsertLifetime) {
initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
}
static char ID; // Pass identification, replacement for typeid
virtual InlineCost getInlineCost(CallSite CS);
virtual bool doFinalization(CallGraph &CG) {
return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
}
virtual bool doInitialization(CallGraph &CG);
};
}
char AlwaysInliner::ID = 0;
INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
"Inliner for always_inline functions", false, false)
INITIALIZE_AG_DEPENDENCY(CallGraph)
INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
"Inliner for always_inline functions", false, false)
Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
return new AlwaysInliner(InsertLifetime);
}
/// \brief Minimal filter to detect invalid constructs for inlining.
static bool isInlineViable(Function &F) {
bool ReturnsTwice =F.getFnAttributes().hasAttribute(Attributes::ReturnsTwice);
for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
// Disallow inlining of functions which contain an indirect branch.
if (isa<IndirectBrInst>(BI->getTerminator()))
return false;
for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;
++II) {
CallSite CS(II);
if (!CS)
continue;
// Disallow recursive calls.
if (&F == CS.getCalledFunction())
return false;
// Disallow calls which expose returns-twice to a function not previously
// attributed as such.
if (!ReturnsTwice && CS.isCall() &&
cast<CallInst>(CS.getInstruction())->canReturnTwice())
return false;
}
}
return true;
}
/// \brief Get the inline cost for the always-inliner.
///
/// The always inliner *only* handles functions which are marked with the
/// attribute to force inlining. As such, it is dramatically simpler and avoids
/// using the powerful (but expensive) inline cost analysis. Instead it uses
/// a very simple and boring direct walk of the instructions looking for
/// impossible-to-inline constructs.
///
/// Note, it would be possible to go to some lengths to cache the information
/// computed here, but as we only expect to do this for relatively few and
/// small functions which have the explicit attribute to force inlining, it is
/// likely not worth it in practice.
InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
Function *Callee = CS.getCalledFunction();
// We assume indirect calls aren't calling an always-inline function.
if (!Callee) return InlineCost::getNever();
// We can't inline calls to external functions.
// FIXME: We shouldn't even get here.
if (Callee->isDeclaration()) return InlineCost::getNever();
// Return never for anything not marked as always inline.
if (!Callee->getFnAttributes().hasAttribute(Attributes::AlwaysInline))
return InlineCost::getNever();
// Do some minimal analysis to preclude non-viable functions.
if (!isInlineViable(*Callee))
return InlineCost::getNever();
// Otherwise, force inlining.
return InlineCost::getAlways();
}
// doInitialization - Initializes the vector of functions that have not
// been annotated with the "always inline" attribute.
bool AlwaysInliner::doInitialization(CallGraph &CG) {
return false;
}
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