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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3467 91177308-0d34-0410-b5e6-96231b3b80d8
157 lines
5.9 KiB
C++
157 lines
5.9 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
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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/BasicAliasAnalysis.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Support/InstVisitor.h"
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#include "llvm/iMemory.h"
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#include "llvm/Constants.h"
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#include "llvm/GlobalValue.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Pass.h"
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// Register the AliasAnalysis interface, providing a nice name to refer to.
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static RegisterAnalysisGroup<AliasAnalysis> X("Alias Analysis");
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// CanModify - Define a little visitor class that is used to check to see if
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// arbitrary chunks of code can modify a specified pointer.
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//
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namespace {
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struct CanModify : public InstVisitor<CanModify, bool> {
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const AliasAnalysis &AA;
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const Value *Ptr;
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CanModify(const AliasAnalysis *aa, const Value *ptr)
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: AA(*aa), Ptr(ptr) {}
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bool visitInvokeInst(InvokeInst &II) {
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return AA.canInvokeModify(II, Ptr);
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}
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bool visitCallInst(CallInst &CI) {
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return AA.canCallModify(CI, Ptr);
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}
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bool visitStoreInst(StoreInst &SI) {
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assert(!SI.hasIndices() && "Only support stores without indexing!");
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return AA.alias(Ptr, SI.getOperand(1));
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}
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// Other instructions do not alias anything.
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bool visitInstruction(Instruction &I) { return false; }
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};
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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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// 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) const {
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CanModify CM(this, Ptr);
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BasicBlock &BB = const_cast<BasicBlock&>(bb);
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for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
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if (CM.visit(I)) // Check every instruction in the basic block...
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return true;
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return false;
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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) const {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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CanModify CM(this, Ptr);
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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)
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if (CM.visit(I)) // Check every instruction in the basic block...
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return true;
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return false;
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}
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//===----------------------------------------------------------------------===//
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// BasicAliasAnalysis Pass Implementation
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//===----------------------------------------------------------------------===//
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//
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// Because of the way .a files work, the implementation of the
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// BasicAliasAnalysis class MUST be in the AliasAnalysis file itself, or else we
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// run the risk of AliasAnalysis being used, but the default implementation not
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// being linked into the tool that uses it. As such, we register and implement
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// the class here.
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//
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namespace {
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// Register this pass...
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RegisterOpt<BasicAliasAnalysis>
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X("basicaa", "Basic Alias Analysis (default AA impl)");
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// Declare that we implement the AliasAnalysis interface
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RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
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} // End of anonymous namespace
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// hasUniqueAddress - Return true if the
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static inline bool hasUniqueAddress(const Value *V) {
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return isa<GlobalValue>(V) || isa<MallocInst>(V) || isa<AllocaInst>(V);
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}
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AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1,
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const Value *V2) const {
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// Strip off constant pointer refs if they exist
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if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V1))
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V1 = CPR->getValue();
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if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V2))
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V2 = CPR->getValue();
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// Are we checking for alias of the same value?
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if (V1 == V2) return MustAlias;
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if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
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return NoAlias; // Scalars cannot alias each other
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bool V1Unique = hasUniqueAddress(V1);
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bool V2Unique = hasUniqueAddress(V2);
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if (V1Unique && V2Unique)
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return NoAlias; // Can't alias if they are different unique values
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if ((V1Unique && isa<ConstantPointerNull>(V2)) ||
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(V2Unique && isa<ConstantPointerNull>(V1)))
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return NoAlias; // Unique values don't alias null
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// TODO: Handle getelementptr with nonzero offset
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return MayAlias;
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}
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