#define DEBUG_TYPE "reassociate"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Constants.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Function.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Pass.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Assembly/Writer.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
using namespace llvm;
assert(Instruction::isAssociative(Opcode) &&
Instruction::isCommutative(Opcode) &&
"Expected an associative and commutative operation!");
- // If we see an absorbing element then the entire expression must be equal to
- // it. For example, if this is a multiplication expression and zero occurs as
- // an operand somewhere in it then the result of the expression must be zero.
- Constant *Absorber = ConstantExpr::getBinOpAbsorber(Opcode, I->getType());
// Visit all operands of the expression, keeping track of their weight (the
// number of paths from the expression root to the operand, or if you like
DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
assert(!Op->use_empty() && "No uses, so how did we get to it?!");
- // If the expression contains an absorbing element then there is no need
- // to analyze it further: it must evaluate to the absorbing element.
- if (Op == Absorber && !Weight.isMinValue()) {
- Ops.push_back(std::make_pair(Absorber, APInt(Bitwidth, 1)));
- return MadeChange;
- }
-
// If this is a binary operation of the right kind with only one use then
// add its operands to the expression.
if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
SmallVectorImpl<ValueEntry> &Ops) {
assert(Ops.size() > 1 && "Single values should be used directly!");
- // Since our optimizations never increase the number of operations, the new
- // expression can always be written by reusing the existing binary operators
+ // Since our optimizations should never increase the number of operations, the
+ // new expression can usually be written reusing the existing binary operators
// from the original expression tree, without creating any new instructions,
// though the rewritten expression may have a completely different topology.
// We take care to not change anything if the new expression will be the same
unsigned Opcode = I->getOpcode();
BinaryOperator *Op = I;
+ /// NotRewritable - The operands being written will be the leaves of the new
+ /// expression and must not be used as inner nodes (via NodesToRewrite) by
+ /// mistake. Inner nodes are always reassociable, and usually leaves are not
+ /// (if they were they would have been incorporated into the expression and so
+ /// would not be leaves), so most of the time there is no danger of this. But
+ /// in rare cases a leaf may become reassociable if an optimization kills uses
+ /// of it, or it may momentarily become reassociable during rewriting (below)
+ /// due it being removed as an operand of one of its uses. Ensure that misuse
+ /// of leaf nodes as inner nodes cannot occur by remembering all of the future
+ /// leaves and refusing to reuse any of them as inner nodes.
+ SmallPtrSet<Value*, 8> NotRewritable;
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+ NotRewritable.insert(Ops[i].Op);
+
// ExpressionChanged - Non-null if the rewritten expression differs from the
// original in some non-trivial way, requiring the clearing of optional flags.
// Flags are cleared from the operator in ExpressionChanged up to I inclusive.
// the old operands with the new ones.
DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewLHS != OldLHS) {
- if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode))
+ BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(0, NewLHS);
}
if (NewRHS != OldRHS) {
- if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode))
+ BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
}
Op->swapOperands();
} else {
// Overwrite with the new right-hand side.
- if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
+ BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
ExpressionChanged = Op;
// Now deal with the left-hand side. If this is already an operation node
// from the original expression then just rewrite the rest of the expression
// into it.
- if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) {
+ BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
+ if (BO && !NotRewritable.count(BO)) {
Op = BO;
continue;
}
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