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fix the regressions from Eric's patch by making GetConstantStringInfo

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tolerate a non-nul-terminated string, and handling a direct global 
reference.

llvm-svn: 52813
This commit is contained in:
Chris Lattner 2008-06-27 03:36:51 +00:00
parent 635da8cff5
commit c94b39d65c
2 changed files with 35 additions and 30 deletions
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2
include/llvm/Analysis/ValueTracking.h
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@ -76,7 +76,7 @@ namespace llvm {
/// GetConstantStringInfo - This function computes the length of a
/// null-terminated C string pointed to by V. If successful, it returns true
/// and returns the string in Str. If unsuccessful, it returns false.
bool GetConstantStringInfo(Value *V, std::string &Str);
bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0);
} // end namespace llvm
#endif

63
lib/Analysis/ValueTracking.cpp
View File

@ -935,13 +935,13 @@ Value *llvm::FindInsertedValue(Value *V, const unsigned *idx_begin,
/// GetConstantStringInfo - This function computes the length of a
/// null-terminated C string pointed to by V. If successful, it returns true
/// and returns the string in Str. If unsuccessful, it returns false.
bool llvm::GetConstantStringInfo(Value *V, std::string &Str) {
bool llvm::GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset) {
// If V is NULL then return false;
if (V == NULL) return false;
// Look through bitcast instructions.
if (BitCastInst *BCI = dyn_cast<BitCastInst>(V))
return GetConstantStringInfo(BCI->getOperand(0), Str);
return GetConstantStringInfo(BCI->getOperand(0), Str, Offset);
// If the value is not a GEP instruction nor a constant expression with a
// GEP instruction, then return false because ConstantArray can't occur
@ -953,35 +953,36 @@ bool llvm::GetConstantStringInfo(Value *V, std::string &Str) {
if (CE->getOpcode() != Instruction::GetElementPtr)
return false;
GEP = CE;
} else {
return false;
}
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
if (ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(1))) {
if (!Idx->isZero())
if (GEP) {
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
} else
return false;
// If the second index isn't a ConstantInt, then this is a variable index
// into the array. If this occurs, we can't say anything meaningful about
// the string.
uint64_t StartIdx = 0;
if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
StartIdx = CI->getZExtValue();
else
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
if (ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(1))) {
if (!Idx->isZero())
return false;
} else
return false;
// If the second index isn't a ConstantInt, then this is a variable index
// into the array. If this occurs, we can't say anything meaningful about
// the string.
uint64_t StartIdx = 0;
if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
StartIdx = CI->getZExtValue();
else
return false;
return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset);
}
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
GlobalVariable* GV = dyn_cast<GlobalVariable>(V);
if (!GV || !GV->isConstant() || !GV->hasInitializer())
return false;
Constant *GlobalInit = GV->getInitializer();
@ -1002,10 +1003,13 @@ bool llvm::GetConstantStringInfo(Value *V, std::string &Str) {
// Get the number of elements in the array
uint64_t NumElts = Array->getType()->getNumElements();
// Traverse the constant array from StartIdx (derived above) which is
// the place the GEP refers to in the array.
Str.reserve(NumElts);
for (unsigned i = StartIdx; i < NumElts; ++i) {
if (Offset > NumElts)
return false;
// Traverse the constant array from 'Offset' which is the place the GEP refers
// to in the array.
Str.reserve(NumElts-Offset);
for (unsigned i = Offset; i != NumElts; ++i) {
Constant *Elt = Array->getOperand(i);
ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
if (!CI) // This array isn't suitable, non-int initializer.
@ -1015,5 +1019,6 @@ bool llvm::GetConstantStringInfo(Value *V, std::string &Str) {
Str += (char)CI->getZExtValue();
}
return false; // The array isn't null terminated.
// The array isn't null terminated, but maybe this is a memcpy, not a strcpy.
return true;
}