Author: lattner
Date: Sun Feb 17 14:44:51 2008
New Revision: 47239
URL: http://llvm.org/viewvc/llvm-project?rev=47239&view=rev
Log:
make the logic for breaking up subtracts more explicit, no
functionality change.
Modified:
llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp?rev=47239&r1=47238&r2=47239&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp Sun Feb 17 14:44:51 2008
@@ -391,17 +391,30 @@
return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
}
+/// ShouldBreakUpSubtract - Return true if we should break up this subtract of
+/// X-Y into (X + -Y).
+static bool ShouldBreakUpSubtract(Instruction *Sub) {
+ // If this is a negation, we can't split it up!
+ if (BinaryOperator::isNeg(Sub))
+ return false;
+
+ // Don't bother to break this up unless either the LHS is an associable add
or
+ // if this is only used by one.
+ if (isReassociableOp(Sub->getOperand(0), Instruction::Add))
+ return true;
+ if (isReassociableOp(Sub->getOperand(1), Instruction::Add))
+ return true;
+
+ if (Sub->hasOneUse() && isReassociableOp(Sub->use_back(), Instruction::Add))
+ return true;
+
+ return false;
+}
+
/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this
is
/// only used by an add, transform this into (X+(0-Y)) to promote better
/// reassociation.
static Instruction *BreakUpSubtract(Instruction *Sub) {
- // Don't bother to break this up unless either the LHS is an associable add
or
- // if this is only used by one.
- if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
- !isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
- !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(),
Instruction::Add)))
- return 0;
-
// Convert a subtract into an add and a neg instruction... so that sub
// instructions can be commuted with other add instructions...
//
@@ -762,12 +775,12 @@
// If this is a subtract instruction which is not already in negate form,
// see if we can convert it to X+-Y.
if (BI->getOpcode() == Instruction::Sub) {
- if (!BinaryOperator::isNeg(BI)) {
+ if (ShouldBreakUpSubtract(BI)) {
if (Instruction *NI = BreakUpSubtract(BI)) {
MadeChange = true;
BI = NI;
}
- } else {
+ } else if (BinaryOperator::isNeg(BI)) {
// Otherwise, this is a negation. See if the operand is a multiply
tree
// and if this is not an inner node of a multiply tree.
if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
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