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| author | Eric Christopher <echristo@apple.com> | 2008-06-26 00:31:12 +0000 |
|---|---|---|
| committer | Eric Christopher <echristo@apple.com> | 2008-06-26 00:31:12 +0000 |
| commit | 3e73cd98c44d52f50e91bbad8267c68c9cdf906e (patch) | |
| tree | c8c5920b98cb731179014d6db62b95062800d8c4 /lib/Analysis/ValueTracking.cpp | |
| parent | 8e0e2bdc2b04f49b23bfced688b02162ea842683 (diff) | |
| download | external_llvm-3e73cd98c44d52f50e91bbad8267c68c9cdf906e.zip external_llvm-3e73cd98c44d52f50e91bbad8267c68c9cdf906e.tar.gz external_llvm-3e73cd98c44d52f50e91bbad8267c68c9cdf906e.tar.bz2 | |
Move GetConstantStringInfo to lib/Analysis. Remove
string output routine from Constant. Update all
callers. Change debug intrinsic api slightly to
accomodate move of routine, these now return values
instead of strings.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52748 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index 32a77e6..3c4e6bc 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -15,6 +15,7 @@ #include "llvm/Analysis/ValueTracking.h" #include "llvm/Constants.h" #include "llvm/Instructions.h" +#include "llvm/GlobalVariable.h" #include "llvm/IntrinsicInst.h" #include "llvm/Target/TargetData.h" #include "llvm/Support/GetElementPtrTypeIterator.h" @@ -930,3 +931,88 @@ Value *llvm::FindInsertedValue(Value *V, const unsigned *idx_begin, // or load instruction) return 0; } + +/// 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) { + // 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); + + // If the value is not a GEP instruction nor a constant expression with a + // GEP instruction, then return false because ConstantArray can't occur + // any other way + User *GEP = 0; + if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) { + GEP = GEPI; + } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { + 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()) + 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; + + // 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)); + if (!GV || !GV->isConstant() || !GV->hasInitializer()) + return false; + Constant *GlobalInit = GV->getInitializer(); + + // Handle the ConstantAggregateZero case + if (isa<ConstantAggregateZero>(GlobalInit)) { + // This is a degenerate case. The initializer is constant zero so the + // length of the string must be zero. + Str.clear(); + return true; + } + + // Must be a Constant Array + ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit); + if (Array == 0 || Array->getType()->getElementType() != Type::Int8Ty) + return false; + + // 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. + for (unsigned i = StartIdx; i < NumElts; ++i) { + Constant *Elt = Array->getOperand(i); + ConstantInt *CI = dyn_cast<ConstantInt>(Elt); + if (!CI) // This array isn't suitable, non-int initializer. + return false; + if (CI->isZero()) + return true; // we found end of string, success! + Str += (char)CI->getZExtValue(); + } + + return false; // The array isn't null terminated. +} |