diff options
Diffstat (limited to 'lib/Analysis')
-rw-r--r-- | lib/Analysis/InstructionSimplify.cpp | 7 | ||||
-rw-r--r-- | lib/Analysis/ScalarEvolutionExpander.cpp | 22 | ||||
-rw-r--r-- | lib/Analysis/ValueTracking.cpp | 129 |
3 files changed, 153 insertions, 5 deletions
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp index 1f8053a..8288e96 100644 --- a/lib/Analysis/InstructionSimplify.cpp +++ b/lib/Analysis/InstructionSimplify.cpp @@ -194,11 +194,10 @@ Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS, const Type *ITy = GetCompareTy(LHS); // icmp X, X -> true/false - if (LHS == RHS) + // X icmp undef -> true/false. For example, icmp ugt %X, undef -> false + // because X could be 0. + if (LHS == RHS || isa<UndefValue>(RHS)) return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred)); - - if (isa<UndefValue>(RHS)) // X icmp undef -> undef - return UndefValue::get(ITy); // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value // addresses never equal each other! We already know that Op0 != Op1. diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp index f5f10c8..e27da96 100644 --- a/lib/Analysis/ScalarEvolutionExpander.cpp +++ b/lib/Analysis/ScalarEvolutionExpander.cpp @@ -15,6 +15,7 @@ #include "llvm/Analysis/ScalarEvolutionExpander.h" #include "llvm/Analysis/LoopInfo.h" +#include "llvm/IntrinsicInst.h" #include "llvm/LLVMContext.h" #include "llvm/Target/TargetData.h" #include "llvm/ADT/STLExtras.h" @@ -137,6 +138,10 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, if (IP != BlockBegin) { --IP; for (; ScanLimit; --IP, --ScanLimit) { + // Don't count dbg.value against the ScanLimit, to avoid perturbing the + // generated code. + if (isa<DbgInfoIntrinsic>(IP)) + ScanLimit++; if (IP->getOpcode() == (unsigned)Opcode && IP->getOperand(0) == LHS && IP->getOperand(1) == RHS) return IP; @@ -505,6 +510,10 @@ Value *SCEVExpander::expandAddToGEP(const SCEV *const *op_begin, if (IP != BlockBegin) { --IP; for (; ScanLimit; --IP, --ScanLimit) { + // Don't count dbg.value against the ScanLimit, to avoid perturbing the + // generated code. + if (isa<DbgInfoIntrinsic>(IP)) + ScanLimit++; if (IP->getOpcode() == Instruction::GetElementPtr && IP->getOperand(0) == V && IP->getOperand(1) == Idx) return IP; @@ -1258,8 +1267,19 @@ Value *SCEVExpander::expand(const SCEV *S) { L = L->getParentLoop()) if (S->isLoopInvariant(L)) { if (!L) break; - if (BasicBlock *Preheader = L->getLoopPreheader()) + if (BasicBlock *Preheader = L->getLoopPreheader()) { InsertPt = Preheader->getTerminator(); + BasicBlock::iterator IP = InsertPt; + // Back past any debug info instructions. Sometimes we inserted + // something earlier before debug info but after any real instructions. + // This should behave the same as if debug info was not present. + while (IP != Preheader->begin()) { + --IP; + if (!isa<DbgInfoIntrinsic>(IP)) + break; + InsertPt = IP; + } + } } else { // If the SCEV is computable at this level, insert it into the header // after the PHIs (and after any other instructions that we've inserted diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index 09344a3..92cbb7c 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -23,6 +23,7 @@ #include "llvm/Target/TargetData.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/MathExtras.h" +#include "llvm/ADT/SmallPtrSet.h" #include <cstring> using namespace llvm; @@ -1436,3 +1437,131 @@ bool llvm::GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset, // The array isn't null terminated, but maybe this is a memcpy, not a strcpy. return true; } + +// These next two are very similar to the above, but also look through PHI +// nodes. +// TODO: See if we can integrate these two together. + +/// GetStringLengthH - If we can compute the length of the string pointed to by +/// the specified pointer, return 'len+1'. If we can't, return 0. +static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) { + // Look through noop bitcast instructions. + if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) + return GetStringLengthH(BCI->getOperand(0), PHIs); + + // If this is a PHI node, there are two cases: either we have already seen it + // or we haven't. + if (PHINode *PN = dyn_cast<PHINode>(V)) { + if (!PHIs.insert(PN)) + return ~0ULL; // already in the set. + + // If it was new, see if all the input strings are the same length. + uint64_t LenSoFar = ~0ULL; + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs); + if (Len == 0) return 0; // Unknown length -> unknown. + + if (Len == ~0ULL) continue; + + if (Len != LenSoFar && LenSoFar != ~0ULL) + return 0; // Disagree -> unknown. + LenSoFar = Len; + } + + // Success, all agree. + return LenSoFar; + } + + // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y) + if (SelectInst *SI = dyn_cast<SelectInst>(V)) { + uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs); + if (Len1 == 0) return 0; + uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs); + if (Len2 == 0) return 0; + if (Len1 == ~0ULL) return Len2; + if (Len2 == ~0ULL) return Len1; + if (Len1 != Len2) return 0; + return Len1; + } + + // If the value is not a GEP instruction nor a constant expression with a + // GEP instruction, then return unknown. + 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 0; + GEP = CE; + } else { + return 0; + } + + // Make sure the GEP has exactly three arguments. + if (GEP->getNumOperands() != 3) + return 0; + + // 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 0; + } else + return 0; + + // 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 0; + + // 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() || + GV->mayBeOverridden()) + return 0; + Constant *GlobalInit = GV->getInitializer(); + + // Handle the ConstantAggregateZero case, which is a degenerate case. The + // initializer is constant zero so the length of the string must be zero. + if (isa<ConstantAggregateZero>(GlobalInit)) + return 1; // Len = 0 offset by 1. + + // Must be a Constant Array + ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit); + if (!Array || !Array->getType()->getElementType()->isIntegerTy(8)) + 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 0; + if (CI->isZero()) + return i-StartIdx+1; // We found end of string, success! + } + + return 0; // The array isn't null terminated, conservatively return 'unknown'. +} + +/// GetStringLength - If we can compute the length of the string pointed to by +/// the specified pointer, return 'len+1'. If we can't, return 0. +uint64_t llvm::GetStringLength(Value *V) { + if (!V->getType()->isPointerTy()) return 0; + + SmallPtrSet<PHINode*, 32> PHIs; + uint64_t Len = GetStringLengthH(V, PHIs); + // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return + // an empty string as a length. + return Len == ~0ULL ? 1 : Len; +} |