/// Assign or look up previously assigned numbers for the two values, and
/// return whether the numbers are equal. Numbers are assigned in the order
/// visited.
- bool enumerate(const Value *V1, const Value *V2);
+ /// Comparison order:
+ /// Stage 0: Value that is function itself is always greater then others.
+ /// If left and right values are references to their functions, then
+ /// they are equal.
+ /// Stage 1: Constants are greater than non-constants.
+ /// If both left and right are constants, then the result of
+ /// cmpConstants is used as cmpValues result.
+ /// Stage 2: InlineAsm instances are greater than others. If both left and
+ /// right are InlineAsm instances, InlineAsm* pointers casted to
+ /// integers and compared as numbers.
+ /// Stage 3: For all other cases we compare order we meet these values in
+ /// their functions. If right value was met first during scanning,
+ /// then left value is greater.
+ /// In another words, we compare serial numbers, for more details
+ /// see comments for sn_mapL and sn_mapR.
+ int cmpValues(const Value *L, const Value *R);
+
+ bool enumerate(const Value *V1, const Value *V2) {
+ return cmpValues(V1, V2) == 0;
+ }
/// Compare two Instructions for equivalence, similar to
/// Instruction::isSameOperationAs but with modifications to the type
const DataLayout *DL;
- DenseMap<const Value *, const Value *> id_map;
- DenseSet<const Value *> seen_values;
+ /// Assign serial numbers to values from left function, and values from
+ /// right function.
+ /// Explanation:
+ /// Being comparing functions we need to compare values we meet at left and
+ /// right sides.
+ /// Its easy to sort things out for external values. It just should be
+ /// the same value at left and right.
+ /// But for local values (those were introduced inside function body)
+ /// we have to ensure they were introduced at exactly the same place,
+ /// and plays the same role.
+ /// Let's assign serial number to each value when we meet it first time.
+ /// Values that were met at same place will be with same serial numbers.
+ /// In this case it would be good to explain few points about values assigned
+ /// to BBs and other ways of implementation (see below).
+ ///
+ /// 1. Safety of BB reordering.
+ /// It's safe to change the order of BasicBlocks in function.
+ /// Relationship with other functions and serial numbering will not be
+ /// changed in this case.
+ /// As follows from FunctionComparator::compare(), we do CFG walk: we start
+ /// from the entry, and then take each terminator. So it doesn't matter how in
+ /// fact BBs are ordered in function. And since cmpValues are called during
+ /// this walk, the numbering depends only on how BBs located inside the CFG.
+ /// So the answer is - yes. We will get the same numbering.
+ ///
+ /// 2. Impossibility to use dominance properties of values.
+ /// If we compare two instruction operands: first is usage of local
+ /// variable AL from function FL, and second is usage of local variable AR
+ /// from FR, we could compare their origins and check whether they are
+ /// defined at the same place.
+ /// But, we are still not able to compare operands of PHI nodes, since those
+ /// could be operands from further BBs we didn't scan yet.
+ /// So it's impossible to use dominance properties in general.
+ DenseMap<const Value*, int> sn_mapL, sn_mapR;
};
}
return true;
}
-// Compare two values used by the two functions under pair-wise comparison. If
-// this is the first time the values are seen, they're added to the mapping so
-// that we will detect mismatches on next use.
-bool FunctionComparator::enumerate(const Value *V1, const Value *V2) {
- // Check for function @f1 referring to itself and function @f2 referring to
- // itself, or referring to each other, or both referring to either of them.
- // They're all equivalent if the two functions are otherwise equivalent.
- if (V1 == F1 && V2 == F2)
- return true;
- if (V1 == F2 && V2 == F1)
- return true;
+/// Compare two values used by the two functions under pair-wise comparison. If
+/// this is the first time the values are seen, they're added to the mapping so
+/// that we will detect mismatches on next use.
+/// See comments in declaration for more details.
+int FunctionComparator::cmpValues(const Value *L, const Value *R) {
+ // Catch self-reference case.
+ if (L == F1) {
+ if (R == F2)
+ return 0;
+ return -1;
+ }
+ if (R == F2) {
+ if (L == F1)
+ return 0;
+ return 1;
+ }
- if (const Constant *C1 = dyn_cast<Constant>(V1)) {
- if (V1 == V2) return true;
- const Constant *C2 = dyn_cast<Constant>(V2);
- if (!C2) return false;
- // TODO: constant expressions with GEP or references to F1 or F2.
- if (C1->isNullValue() && C2->isNullValue() &&
- isEquivalentType(C1->getType(), C2->getType()))
- return true;
-
- // Compare constants:
- // Check whether type of C1 is bitcastable to C2's type.
- // If the bitcast is possible then compare raw constants contents.
- return cmpConstants(C1, C2) == 0;
+ const Constant *ConstL = dyn_cast<Constant>(L);
+ const Constant *ConstR = dyn_cast<Constant>(R);
+ if (ConstL && ConstR) {
+ if (L == R)
+ return 0;
+ return cmpConstants(ConstL, ConstR);
}
- if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2))
- return V1 == V2;
+ if (ConstL)
+ return 1;
+ if (ConstR)
+ return -1;
+
+ const InlineAsm *InlineAsmL = dyn_cast<InlineAsm>(L);
+ const InlineAsm *InlineAsmR = dyn_cast<InlineAsm>(R);
+
+ if (InlineAsmL && InlineAsmR)
+ return cmpNumbers((uint64_t)L, (uint64_t)R);
+ if (InlineAsmL)
+ return 1;
+ if (InlineAsmR)
+ return -1;
- // Check that V1 maps to V2. If we find a value that V1 maps to then we simply
- // check whether it's equal to V2. When there is no mapping then we need to
- // ensure that V2 isn't already equivalent to something else. For this
- // purpose, we track the V2 values in a set.
+ auto LeftSN = sn_mapL.insert(std::make_pair(L, sn_mapL.size())),
+ RightSN = sn_mapR.insert(std::make_pair(R, sn_mapR.size()));
- const Value *&map_elem = id_map[V1];
- if (map_elem)
- return map_elem == V2;
- if (!seen_values.insert(V2).second)
- return false;
- map_elem = V2;
- return true;
+ return cmpNumbers(LeftSN.first->second, RightSN.first->second);
}
-
// Test whether two basic blocks have equivalent behaviour.
bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) {
BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
// We need to recheck everything, but check the things that weren't included
// in the hash first.
+ sn_mapL.clear();
+ sn_mapR.clear();
+
if (F1->getAttributes() != F2->getAttributes())
return false;