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The meaning of getTypeSize was not clear - clarifying it is important now that we have x86 long double and arbitrary precision integers. The issue with long double is that it requires 80 bits, and this is not a multiple of its alignment. This gives a primitive type for which getTypeSize differed from getABITypeSize. For arbitrary precision integers it is even worse: there is the minimum number of bits needed to hold the type (eg: 36 for an i36), the maximum number of bits that will be overwriten when storing the type (40 bits for i36) and the ABI size (i.e. the storage size rounded up to a multiple of the alignment; 64 bits for i36). This patch removes getTypeSize (not really - it is still there but deprecated to allow for a gradual transition). Instead there is: (1) getTypeSizeInBits - a number of bits that suffices to hold all values of the type. For a primitive type, this is the minimum number of bits. For an i36 this is 36 bits. For x86 long double it is 80. This corresponds to gcc's TYPE_PRECISION. (2) getTypeStoreSizeInBits - the maximum number of bits that is written when storing the type (or read when reading it). For an i36 this is 40 bits, for an x86 long double it is 80 bits. This is the size alias analysis is interested in (getTypeStoreSize returns the number of bytes). There doesn't seem to be anything corresponding to this in gcc. (3) getABITypeSizeInBits - this is getTypeStoreSizeInBits rounded up to a multiple of the alignment. For an i36 this is 64, for an x86 long double this is 96 or 128 depending on the OS. This is the spacing between consecutive elements when you form an array out of this type (getABITypeSize returns the number of bytes). This is TYPE_SIZE in gcc. Since successive elements in a SequentialType (arrays, pointers and vectors) need to be aligned, the spacing between them will be given by getABITypeSize. This means that the size of an array is the length times the getABITypeSize. It also means that GEP computations need to use getABITypeSize when computing offsets. Furthermore, if an alloca allocates several elements at once then these too need to be aligned, so the size of the alloca has to be the number of elements multiplied by getABITypeSize. Logically speaking this doesn't have to be the case when allocating just one element, but it is simpler to also use getABITypeSize in this case. So alloca's and mallocs should use getABITypeSize. Finally, since gcc's only notion of size is that given by getABITypeSize, if you want to output assembler etc the same as gcc then getABITypeSize is the size you want. Since a store will overwrite no more than getTypeStoreSize bytes, and a read will read no more than that many bytes, this is the notion of size appropriate for alias analysis calculations. In this patch I have corrected all type size uses except some of those in ScalarReplAggregates, lib/Codegen, lib/Target (the hard cases). I will get around to auditing these too at some point, but I could do with some help. Finally, I made one change which I think wise but others might consider pointless and suboptimal: in an unpacked struct the amount of space allocated for a field is now given by the ABI size rather than getTypeStoreSize. I did this because every other place that reserves memory for a type (eg: alloca) now uses getABITypeSize, and I didn't want to make an exception for unpacked structs, i.e. I did it to make things more uniform. This only effects structs containing long doubles and arbitrary precision integers. If someone wants to pack these types more tightly they can always use a packed struct. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43620 91177308-0d34-0410-b5e6-96231b3b80d8
192 lines
7.5 KiB
C++
192 lines
7.5 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the generic AliasAnalysis interface which is used as the
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// common interface used by all clients and implementations of alias analysis.
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//
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// This file also implements the default version of the AliasAnalysis interface
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// that is to be used when no other implementation is specified. This does some
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// simple tests that detect obvious cases: two different global pointers cannot
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// alias, a global cannot alias a malloc, two different mallocs cannot alias,
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// etc.
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//
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// This alias analysis implementation really isn't very good for anything, but
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// it is very fast, and makes a nice clean default implementation. Because it
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// handles lots of little corner cases, other, more complex, alias analysis
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// implementations may choose to rely on this pass to resolve these simple and
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// easy cases.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Pass.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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// Register the AliasAnalysis interface, providing a nice name to refer to.
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namespace {
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RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
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}
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char AliasAnalysis::ID = 0;
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//===----------------------------------------------------------------------===//
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// Default chaining methods
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//===----------------------------------------------------------------------===//
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AliasAnalysis::AliasResult
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AliasAnalysis::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->alias(V1, V1Size, V2, V2Size);
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}
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void AliasAnalysis::getMustAliases(Value *P, std::vector<Value*> &RetVals) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getMustAliases(P, RetVals);
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}
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bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->pointsToConstantMemory(P);
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
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std::vector<PointerAccessInfo> *Info) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getModRefBehavior(F, CS, Info);
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}
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bool AliasAnalysis::hasNoModRefInfoForCalls() const {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->hasNoModRefInfoForCalls();
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}
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void AliasAnalysis::deleteValue(Value *V) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->deleteValue(V);
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}
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void AliasAnalysis::copyValue(Value *From, Value *To) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->copyValue(From, To);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
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// FIXME: we can do better.
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getModRefInfo(CS1, CS2);
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}
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//===----------------------------------------------------------------------===//
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// AliasAnalysis non-virtual helper method implementation
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//===----------------------------------------------------------------------===//
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
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return alias(L->getOperand(0), TD->getTypeStoreSize(L->getType()),
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P, Size) ? Ref : NoModRef;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
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// If the stored address cannot alias the pointer in question, then the
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// pointer cannot be modified by the store.
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if (!alias(S->getOperand(1),
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TD->getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
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return NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have been
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// modified by this store.
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return pointsToConstantMemory(P) ? NoModRef : Mod;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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ModRefResult Mask = ModRef;
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if (Function *F = CS.getCalledFunction()) {
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ModRefBehavior MRB = getModRefBehavior(F, CallSite());
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if (MRB == OnlyReadsMemory)
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Mask = Ref;
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else if (MRB == DoesNotAccessMemory)
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return NoModRef;
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}
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if (!AA) return Mask;
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// If P points to a constant memory location, the call definitely could not
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// modify the memory location.
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if ((Mask & Mod) && AA->pointsToConstantMemory(P))
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Mask = ModRefResult(Mask & ~Mod);
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return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
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}
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// AliasAnalysis destructor: DO NOT move this to the header file for
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// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
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// the AliasAnalysis.o file in the current .a file, causing alias analysis
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// support to not be included in the tool correctly!
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//
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AliasAnalysis::~AliasAnalysis() {}
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/// setTargetData - Subclasses must call this method to initialize the
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/// AliasAnalysis interface before any other methods are called.
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///
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void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
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TD = &P->getAnalysis<TargetData>();
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AA = &P->getAnalysis<AliasAnalysis>();
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}
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// getAnalysisUsage - All alias analysis implementations should invoke this
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// directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
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// TargetData is required by the pass.
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void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetData>(); // All AA's need TargetData.
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AU.addRequired<AliasAnalysis>(); // All AA's chain
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}
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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the value pointed to by Ptr.
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///
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bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
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const Value *Ptr, unsigned Size) {
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return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
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}
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/// canInstructionRangeModify - Return true if it is possible for the execution
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/// of the specified instructions to modify the value pointed to by Ptr. The
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/// instructions to consider are all of the instructions in the range of [I1,I2]
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/// INCLUSIVE. I1 and I2 must be in the same basic block.
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///
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bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
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const Instruction &I2,
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const Value *Ptr, unsigned Size) {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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BasicBlock::iterator I = const_cast<Instruction*>(&I1);
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BasicBlock::iterator E = const_cast<Instruction*>(&I2);
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++E; // Convert from inclusive to exclusive range.
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for (; I != E; ++I) // Check every instruction in range
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if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
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return true;
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return false;
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}
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// Because of the way .a files work, we must force the BasicAA implementation to
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// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
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// the risk of AliasAnalysis being used, but the default implementation not
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// being linked into the tool that uses it.
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DEFINING_FILE_FOR(AliasAnalysis)
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