[llvm] r208189  MergeFunctions Pass, introduced total ordering among values.
Stepan Dyatkovskiy
stpworld at narod.ru
Wed May 7 04:11:40 PDT 2014
Author: dyatkovskiy
Date: Wed May 7 06:11:39 2014
New Revision: 208189
URL: http://llvm.org/viewvc/llvmproject?rev=208189&view=rev
Log:
MergeFunctions Pass, introduced total ordering among values.
This is a third patch of patch series that improves MergeFunctions
performance time from O(N*N) to O(N*log(N)).
This patch description:
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.
In short, patch introduces values serial numbering and comparison routine.
The last one compares two values by their serial numbers.
Modified:
llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
Modified: llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
URL: http://llvm.org/viewvc/llvmproject/llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp?rev=208189&r1=208188&r2=208189&view=diff
==============================================================================
 llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp Wed May 7 06:11:39 2014
@@ 283,7 +283,26 @@ private:
/// 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 nonconstants.
+ /// 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
@@ 354,8 +373,40 @@ private:
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;
};
}
@@ 718,50 +769,51 @@ bool FunctionComparator::isEquivalentGEP
return true;
}
// Compare two values used by the two functions under pairwise 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;

 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;
 }

 if (isa<InlineAsm>(V1)  isa<InlineAsm>(V2))
 return V1 == V2;

 // 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.

 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;
}
+/// Compare two values used by the two functions under pairwise 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 selfreference case.
+ if (L == F1) {
+ if (R == F2)
+ return 0;
+ return 1;
+ }
+ if (R == F2) {
+ if (L == F1)
+ return 0;
+ return 1;
+ }
+
+ 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 (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;
+ auto LeftSN = sn_mapL.insert(std::make_pair(L, sn_mapL.size())),
+ RightSN = sn_mapR.insert(std::make_pair(R, sn_mapR.size()));
+
+ 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();
@@ 810,6 +862,9 @@ bool FunctionComparator::compare() {
// 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;
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