mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-30 21:29:28 +00:00
reference to a pointer, so that it can handle the case where DataLayout is not available and behave conservatively. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174024 91177308-0d34-0410-b5e6-96231b3b80d8
222 lines
8.6 KiB
C++
222 lines
8.6 KiB
C++
//===- Loads.cpp - Local load analysis ------------------------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file defines simple local analyses for load instructions.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Analysis/Loads.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Analysis/ValueTracking.h"
|
|
#include "llvm/IR/DataLayout.h"
|
|
#include "llvm/IR/GlobalAlias.h"
|
|
#include "llvm/IR/GlobalVariable.h"
|
|
#include "llvm/IR/IntrinsicInst.h"
|
|
#include "llvm/IR/LLVMContext.h"
|
|
#include "llvm/IR/Operator.h"
|
|
using namespace llvm;
|
|
|
|
/// AreEquivalentAddressValues - Test if A and B will obviously have the same
|
|
/// value. This includes recognizing that %t0 and %t1 will have the same
|
|
/// value in code like this:
|
|
/// %t0 = getelementptr \@a, 0, 3
|
|
/// store i32 0, i32* %t0
|
|
/// %t1 = getelementptr \@a, 0, 3
|
|
/// %t2 = load i32* %t1
|
|
///
|
|
static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
|
|
// Test if the values are trivially equivalent.
|
|
if (A == B) return true;
|
|
|
|
// Test if the values come from identical arithmetic instructions.
|
|
// Use isIdenticalToWhenDefined instead of isIdenticalTo because
|
|
// this function is only used when one address use dominates the
|
|
// other, which means that they'll always either have the same
|
|
// value or one of them will have an undefined value.
|
|
if (isa<BinaryOperator>(A) || isa<CastInst>(A) ||
|
|
isa<PHINode>(A) || isa<GetElementPtrInst>(A))
|
|
if (const Instruction *BI = dyn_cast<Instruction>(B))
|
|
if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
|
|
return true;
|
|
|
|
// Otherwise they may not be equivalent.
|
|
return false;
|
|
}
|
|
|
|
/// isSafeToLoadUnconditionally - Return true if we know that executing a load
|
|
/// from this value cannot trap. If it is not obviously safe to load from the
|
|
/// specified pointer, we do a quick local scan of the basic block containing
|
|
/// ScanFrom, to determine if the address is already accessed.
|
|
bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
|
|
unsigned Align, const DataLayout *TD) {
|
|
int64_t ByteOffset = 0;
|
|
Value *Base = V;
|
|
Base = GetPointerBaseWithConstantOffset(V, ByteOffset, TD);
|
|
|
|
if (ByteOffset < 0) // out of bounds
|
|
return false;
|
|
|
|
Type *BaseType = 0;
|
|
unsigned BaseAlign = 0;
|
|
if (const AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
|
|
// An alloca is safe to load from as load as it is suitably aligned.
|
|
BaseType = AI->getAllocatedType();
|
|
BaseAlign = AI->getAlignment();
|
|
} else if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
|
|
// Global variables are safe to load from but their size cannot be
|
|
// guaranteed if they are overridden.
|
|
if (!GV->mayBeOverridden()) {
|
|
BaseType = GV->getType()->getElementType();
|
|
BaseAlign = GV->getAlignment();
|
|
}
|
|
}
|
|
|
|
if (BaseType && BaseType->isSized()) {
|
|
if (TD && BaseAlign == 0)
|
|
BaseAlign = TD->getPrefTypeAlignment(BaseType);
|
|
|
|
if (Align <= BaseAlign) {
|
|
if (!TD)
|
|
return true; // Loading directly from an alloca or global is OK.
|
|
|
|
// Check if the load is within the bounds of the underlying object.
|
|
PointerType *AddrTy = cast<PointerType>(V->getType());
|
|
uint64_t LoadSize = TD->getTypeStoreSize(AddrTy->getElementType());
|
|
if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType) &&
|
|
(Align == 0 || (ByteOffset % Align) == 0))
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// Otherwise, be a little bit aggressive by scanning the local block where we
|
|
// want to check to see if the pointer is already being loaded or stored
|
|
// from/to. If so, the previous load or store would have already trapped,
|
|
// so there is no harm doing an extra load (also, CSE will later eliminate
|
|
// the load entirely).
|
|
BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin();
|
|
|
|
while (BBI != E) {
|
|
--BBI;
|
|
|
|
// If we see a free or a call which may write to memory (i.e. which might do
|
|
// a free) the pointer could be marked invalid.
|
|
if (isa<CallInst>(BBI) && BBI->mayWriteToMemory() &&
|
|
!isa<DbgInfoIntrinsic>(BBI))
|
|
return false;
|
|
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
|
|
if (AreEquivalentAddressValues(LI->getOperand(0), V)) return true;
|
|
} else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
|
|
if (AreEquivalentAddressValues(SI->getOperand(1), V)) return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the
|
|
/// instruction before ScanFrom) checking to see if we have the value at the
|
|
/// memory address *Ptr locally available within a small number of instructions.
|
|
/// If the value is available, return it.
|
|
///
|
|
/// If not, return the iterator for the last validated instruction that the
|
|
/// value would be live through. If we scanned the entire block and didn't find
|
|
/// something that invalidates *Ptr or provides it, ScanFrom would be left at
|
|
/// begin() and this returns null. ScanFrom could also be left
|
|
///
|
|
/// MaxInstsToScan specifies the maximum instructions to scan in the block. If
|
|
/// it is set to 0, it will scan the whole block. You can also optionally
|
|
/// specify an alias analysis implementation, which makes this more precise.
|
|
///
|
|
/// If TBAATag is non-null and a load or store is found, the TBAA tag from the
|
|
/// load or store is recorded there. If there is no TBAA tag or if no access
|
|
/// is found, it is left unmodified.
|
|
Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
|
|
BasicBlock::iterator &ScanFrom,
|
|
unsigned MaxInstsToScan,
|
|
AliasAnalysis *AA,
|
|
MDNode **TBAATag) {
|
|
if (MaxInstsToScan == 0) MaxInstsToScan = ~0U;
|
|
|
|
// If we're using alias analysis to disambiguate get the size of *Ptr.
|
|
uint64_t AccessSize = 0;
|
|
if (AA) {
|
|
Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType();
|
|
AccessSize = AA->getTypeStoreSize(AccessTy);
|
|
}
|
|
|
|
while (ScanFrom != ScanBB->begin()) {
|
|
// We must ignore debug info directives when counting (otherwise they
|
|
// would affect codegen).
|
|
Instruction *Inst = --ScanFrom;
|
|
if (isa<DbgInfoIntrinsic>(Inst))
|
|
continue;
|
|
|
|
// Restore ScanFrom to expected value in case next test succeeds
|
|
ScanFrom++;
|
|
|
|
// Don't scan huge blocks.
|
|
if (MaxInstsToScan-- == 0) return 0;
|
|
|
|
--ScanFrom;
|
|
// If this is a load of Ptr, the loaded value is available.
|
|
// (This is true even if the load is volatile or atomic, although
|
|
// those cases are unlikely.)
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
|
|
if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) {
|
|
if (TBAATag) *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
|
|
return LI;
|
|
}
|
|
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
|
|
// If this is a store through Ptr, the value is available!
|
|
// (This is true even if the store is volatile or atomic, although
|
|
// those cases are unlikely.)
|
|
if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) {
|
|
if (TBAATag) *TBAATag = SI->getMetadata(LLVMContext::MD_tbaa);
|
|
return SI->getOperand(0);
|
|
}
|
|
|
|
// If Ptr is an alloca and this is a store to a different alloca, ignore
|
|
// the store. This is a trivial form of alias analysis that is important
|
|
// for reg2mem'd code.
|
|
if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) &&
|
|
(isa<AllocaInst>(SI->getOperand(1)) ||
|
|
isa<GlobalVariable>(SI->getOperand(1))))
|
|
continue;
|
|
|
|
// If we have alias analysis and it says the store won't modify the loaded
|
|
// value, ignore the store.
|
|
if (AA &&
|
|
(AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
|
|
continue;
|
|
|
|
// Otherwise the store that may or may not alias the pointer, bail out.
|
|
++ScanFrom;
|
|
return 0;
|
|
}
|
|
|
|
// If this is some other instruction that may clobber Ptr, bail out.
|
|
if (Inst->mayWriteToMemory()) {
|
|
// If alias analysis claims that it really won't modify the load,
|
|
// ignore it.
|
|
if (AA &&
|
|
(AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0)
|
|
continue;
|
|
|
|
// May modify the pointer, bail out.
|
|
++ScanFrom;
|
|
return 0;
|
|
}
|
|
}
|
|
|
|
// Got to the start of the block, we didn't find it, but are done for this
|
|
// block.
|
|
return 0;
|
|
}
|