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-rw-r--r--lib/Analysis/Loads.cpp182
1 files changed, 111 insertions, 71 deletions
diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp
index 005d309..bb0d60e 100644
--- a/lib/Analysis/Loads.cpp
+++ b/lib/Analysis/Loads.cpp
@@ -22,25 +22,29 @@
#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
+/// \brief 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:
+/// \code
/// %t0 = getelementptr \@a, 0, 3
/// store i32 0, i32* %t0
/// %t1 = getelementptr \@a, 0, 3
/// %t2 = load i32* %t1
+/// \endcode
///
static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
// Test if the values are trivially equivalent.
- if (A == B) return true;
+ 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 (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;
@@ -49,15 +53,19 @@ static bool AreEquivalentAddressValues(const Value *A, const Value *B) {
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.
+/// \brief Check if executing a load of this pointer 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 \c ScanFrom, to determine
+/// if the address is already accessed.
+///
+/// This uses the pointee type to determine how many bytes need to be safe to
+/// load from the pointer.
bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
- unsigned Align, const DataLayout *TD) {
+ unsigned Align, const DataLayout *DL) {
int64_t ByteOffset = 0;
Value *Base = V;
- Base = GetPointerBaseWithConstantOffset(V, ByteOffset, TD);
+ Base = GetPointerBaseWithConstantOffset(V, ByteOffset, DL);
if (ByteOffset < 0) // out of bounds
return false;
@@ -69,26 +77,29 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
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.
+ // Global variables are not necessarily safe to load from if they are
+ // overridden. Their size may change or they may be weak and require a test
+ // to determine if they were in fact provided.
if (!GV->mayBeOverridden()) {
BaseType = GV->getType()->getElementType();
BaseAlign = GV->getAlignment();
}
}
- if (BaseType && BaseType->isSized()) {
- if (TD && BaseAlign == 0)
- BaseAlign = TD->getPrefTypeAlignment(BaseType);
+ PointerType *AddrTy = cast<PointerType>(V->getType());
+ uint64_t LoadSize = DL ? DL->getTypeStoreSize(AddrTy->getElementType()) : 0;
- if (Align <= BaseAlign) {
- if (!TD)
- return true; // Loading directly from an alloca or global is OK.
+ // If we found a base allocated type from either an alloca or global variable,
+ // try to see if we are definitively within the allocated region. We need to
+ // know the size of the base type and the loaded type to do anything in this
+ // case, so only try this when we have the DataLayout available.
+ if (BaseType && BaseType->isSized() && DL) {
+ if (BaseAlign == 0)
+ BaseAlign = DL->getPrefTypeAlignment(BaseType);
+ if (Align <= BaseAlign) {
// 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) &&
+ if (ByteOffset + LoadSize <= DL->getTypeAllocSize(BaseType) &&
(Align == 0 || (ByteOffset % Align) == 0))
return true;
}
@@ -101,6 +112,10 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
// the load entirely).
BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin();
+ // We can at least always strip pointer casts even though we can't use the
+ // base here.
+ V = V->stripPointerCasts();
+
while (BBI != E) {
--BBI;
@@ -110,46 +125,62 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
!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;
- }
+ Value *AccessedPtr;
+ if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
+ AccessedPtr = LI->getPointerOperand();
+ else if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
+ AccessedPtr = SI->getPointerOperand();
+ else
+ continue;
+
+ // Handle trivial cases even w/o DataLayout or other work.
+ if (AccessedPtr == V)
+ return true;
+
+ if (!DL)
+ continue;
+
+ auto *AccessedTy = cast<PointerType>(AccessedPtr->getType());
+ if (AreEquivalentAddressValues(AccessedPtr->stripPointerCasts(), V) &&
+ LoadSize <= DL->getTypeStoreSize(AccessedTy->getElementType()))
+ 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
+/// \brief Scan the ScanBB block backwards 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
+/// The scan starts from \c ScanFrom. \c MaxInstsToScan specifies the maximum
+/// instructions to scan in the block. If it is set to \c 0, it will scan the whole
+/// block.
+///
+/// If the value is available, this function returns it. If not, it returns 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 \c *Ptr or provides it, \c ScanFrom is left at the last
+/// instruction processed and this returns null.
///
-/// 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.
+/// 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.
+/// If \c AATags is non-null and a load or store is found, the AA tags from the
+/// load or store are recorded there. If there are no AA tags 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;
+ AliasAnalysis *AA, AAMDNodes *AATags) {
+ if (MaxInstsToScan == 0)
+ MaxInstsToScan = ~0U;
+
+ Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType();
// 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);
- }
-
+ uint64_t AccessSize = AA ? AA->getTypeStoreSize(AccessTy) : 0;
+
+ Value *StrippedPtr = Ptr->stripPointerCasts();
+
while (ScanFrom != ScanBB->begin()) {
// We must ignore debug info directives when counting (otherwise they
// would affect codegen).
@@ -159,62 +190,71 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
// Restore ScanFrom to expected value in case next test succeeds
ScanFrom++;
-
+
// Don't scan huge blocks.
- if (MaxInstsToScan-- == 0) return nullptr;
-
+ if (MaxInstsToScan-- == 0)
+ return nullptr;
+
--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);
+ if (AreEquivalentAddressValues(
+ LI->getPointerOperand()->stripPointerCasts(), StrippedPtr) &&
+ CastInst::isBitCastable(LI->getType(), AccessTy)) {
+ if (AATags)
+ LI->getAAMetadata(*AATags);
return LI;
}
-
+
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ Value *StorePtr = SI->getPointerOperand()->stripPointerCasts();
// 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);
+ if (AreEquivalentAddressValues(StorePtr, StrippedPtr) &&
+ CastInst::isBitCastable(SI->getValueOperand()->getType(), AccessTy)) {
+ if (AATags)
+ SI->getAAMetadata(*AATags);
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))))
+
+ // If both StrippedPtr and StorePtr reach all the way to an alloca or
+ // global and they are different, ignore the store. This is a trivial form
+ // of alias analysis that is important for reg2mem'd code.
+ if ((isa<AllocaInst>(StrippedPtr) || isa<GlobalVariable>(StrippedPtr)) &&
+ (isa<AllocaInst>(StorePtr) || isa<GlobalVariable>(StorePtr)) &&
+ StrippedPtr != StorePtr)
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)
+ (AA->getModRefInfo(SI, StrippedPtr, AccessSize) &
+ AliasAnalysis::Mod) == 0)
continue;
-
+
// Otherwise the store that may or may not alias the pointer, bail out.
++ScanFrom;
return nullptr;
}
-
+
// 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)
+ (AA->getModRefInfo(Inst, StrippedPtr, AccessSize) &
+ AliasAnalysis::Mod) == 0)
continue;
-
+
// May modify the pointer, bail out.
++ScanFrom;
return nullptr;
}
}
-
+
// Got to the start of the block, we didn't find it, but are done for this
// block.
return nullptr;
generated by cgit v1.1 at 2024-05-17 22:04:18 +0000