From 621d33bbc08bd309cdabce5901b450116950014a Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Wed, 7 May 2008 19:53:05 +0000 Subject: [PATCH] Add a new LibCallAliasAnalysis pass, which is parameterized by an instance of LibCallInfo to provide mod/ref info of standard library functions. This is powerful enough to say that 'sqrt' is readonly except that it modifies errno, or that "printf doesn't store to memory unless the %n constraint is present" etc. llvm-svn: 50827 --- llvm/include/llvm/Analysis/Passes.h | 9 ++ llvm/include/llvm/LinkAllPasses.h | 1 + llvm/lib/Analysis/LibCallAliasAnalysis.cpp | 169 +++++++++++++++++++++ 3 files changed, 179 insertions(+) create mode 100644 llvm/lib/Analysis/LibCallAliasAnalysis.cpp diff --git a/llvm/include/llvm/Analysis/Passes.h b/llvm/include/llvm/Analysis/Passes.h index cf52831bace1..7843aea2aea1 100644 --- a/llvm/include/llvm/Analysis/Passes.h +++ b/llvm/include/llvm/Analysis/Passes.h @@ -20,6 +20,7 @@ namespace llvm { class ImmutablePass; class ModulePass; class Pass; + class LibCallInfo; //===--------------------------------------------------------------------===// // @@ -61,6 +62,14 @@ namespace llvm { // ImmutablePass *createBasicAliasAnalysisPass(); + //===--------------------------------------------------------------------===// + // + /// createLibCallAliasAnalysisPass - Create an alias analysis pass that knows + /// about the semantics of a set of libcalls specified by LCI. The newly + /// constructed pass takes ownership of the pointer that is provided. + /// + FunctionPass *createLibCallAliasAnalysisPass(LibCallInfo *LCI); + //===--------------------------------------------------------------------===// // // createAndersensPass - This pass implements Andersen's interprocedural alias diff --git a/llvm/include/llvm/LinkAllPasses.h b/llvm/include/llvm/LinkAllPasses.h index ec6e7023dcb0..96f9eaee175a 100644 --- a/llvm/include/llvm/LinkAllPasses.h +++ b/llvm/include/llvm/LinkAllPasses.h @@ -48,6 +48,7 @@ namespace { (void) llvm::createArgumentPromotionPass(); (void) llvm::createStructRetPromotionPass(); (void) llvm::createBasicAliasAnalysisPass(); + (void) llvm::createLibCallAliasAnalysisPass(0); (void) llvm::createBasicVNPass(); (void) llvm::createBlockPlacementPass(); (void) llvm::createBlockProfilerPass(); diff --git a/llvm/lib/Analysis/LibCallAliasAnalysis.cpp b/llvm/lib/Analysis/LibCallAliasAnalysis.cpp new file mode 100644 index 000000000000..6492ac69b518 --- /dev/null +++ b/llvm/lib/Analysis/LibCallAliasAnalysis.cpp @@ -0,0 +1,169 @@ +//===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the LibCallAliasAnalysis class. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/Passes.h" +#include "llvm/Analysis/LibCallSemantics.h" +#include "llvm/Function.h" +#include "llvm/Pass.h" +#include "llvm/Target/TargetData.h" +using namespace llvm; + +namespace llvm { + /// LibCallAliasAnalysis - Alias analysis driven from LibCallInfo. + struct LibCallAliasAnalysis : public FunctionPass, AliasAnalysis { + static char ID; // Class identification + + LibCallInfo *LCI; + + LibCallAliasAnalysis(LibCallInfo *LC = 0) + : FunctionPass((intptr_t)&ID), LCI(LC) { + } + ~LibCallAliasAnalysis() { + delete LCI; + } + + ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); + ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { + // TODO: Could compare two direct calls against each other if we cared to. + return AliasAnalysis::getModRefInfo(CS1,CS2); + } + + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AliasAnalysis::getAnalysisUsage(AU); + AU.addRequired(); + AU.setPreservesAll(); // Does not transform code + } + + virtual bool runOnFunction(Function &F) { + InitializeAliasAnalysis(this); // set up super class + return false; + } + + /// hasNoModRefInfoForCalls - We can provide mod/ref information against + /// non-escaping allocations. + virtual bool hasNoModRefInfoForCalls() const { return false; } + private: + ModRefResult AnalyzeLibCallDetails(const LibCallFunctionInfo *FI, + CallSite CS, Value *P, unsigned Size); + }; + + // Register this pass... + char LibCallAliasAnalysis::ID = 0; + RegisterPass + X("libcall-aa", "LibCall Alias Analysis", false, true); + + // Declare that we implement the AliasAnalysis interface + RegisterAnalysisGroup Y(X); +} // End of llvm namespace + +FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) { + return new LibCallAliasAnalysis(LCI); +} + + +/// AnalyzeLibCallDetails - Given a call to a function with the specified +/// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call +/// vs the specified pointer/size. +AliasAnalysis::ModRefResult +LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI, + CallSite CS, Value *P, + unsigned Size) { + // If we have a function, check to see what kind of mod/ref effects it + // has. Start by including any info globally known about the function. + AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior; + if (MRInfo == NoModRef) return MRInfo; + + // If that didn't tell us that the function is 'readnone', check to see + // if we have detailed info and if 'P' is any of the locations we know + // about. + const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails; + if (Details == 0) + return MRInfo; + + // If the details array is of the 'DoesNot' kind, we only know something if + // the pointer is a match for one of the locations in 'Details'. If we find a + // match, we can prove some interactions cannot happen. + // + if (FI->DetailsType == LibCallFunctionInfo::DoesNot) { + // Find out if the pointer refers to a known location. + for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) { + const LibCallLocationInfo &Loc = + LCI->getLocationInfo(Details[i].LocationID); + LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size); + if (Res != LibCallLocationInfo::Yes) continue; + + // If we find a match against a location that we 'do not' interact with, + // learn this info into MRInfo. + return ModRefResult(MRInfo & ~Details[i].MRInfo); + } + return MRInfo; + } + + // If the details are of the 'DoesOnly' sort, we know something if the pointer + // is a match for one of the locations in 'Details'. Also, if we can prove + // that the pointers is *not* one of the locations in 'Details', we know that + // the call is NoModRef. + assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly); + + // Find out if the pointer refers to a known location. + bool NoneMatch = true; + for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) { + const LibCallLocationInfo &Loc = + LCI->getLocationInfo(Details[i].LocationID); + LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size); + if (Res == LibCallLocationInfo::No) continue; + + // If we don't know if this pointer points to the location, then we have to + // assume it might alias in some case. + if (Res == LibCallLocationInfo::Unknown) { + NoneMatch = false; + continue; + } + + // If we know that this pointer definitely is pointing into the location, + // merge in this information. + return ModRefResult(MRInfo & Details[i].MRInfo); + } + + // If we found that the pointer is guaranteed to not match any of the + // locations in our 'DoesOnly' rule, then we know that the pointer must point + // to some other location. Since the libcall doesn't mod/ref any other + // locations, return NoModRef. + if (NoneMatch) + return NoModRef; + + // Otherwise, return any other info gained so far. + return MRInfo; +} + +// getModRefInfo - Check to see if the specified callsite can clobber the +// specified memory object. +// +AliasAnalysis::ModRefResult +LibCallAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { + ModRefResult MRInfo = ModRef; + + // If this is a direct call to a function that LCI knows about, get the + // information about the runtime function. + if (Function *F = CS.getCalledFunction()) { + if (LCI && F->isDeclaration()) { + if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) { + MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, P, Size)); + if (MRInfo == NoModRef) return NoModRef; + } + } + } + + // The AliasAnalysis base class has some smarts, lets use them. + return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, P, Size)); +}