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allow pushing icmps through phis with multiple uses and across critical edges.

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These are important to push up to encourage jump threading.  This shrinks 176.gcc a bit.

llvm-svn: 82923
This commit is contained in:
Chris Lattner 2009-09-27 20:46:36 +00:00
parent f7db1f1a3a
commit 7a9e470ddc
1 changed files with 23 additions and 8 deletions
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31
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -388,7 +388,11 @@ namespace {
// which has a PHI node as operand #0, see if we can fold the instruction
// into the PHI (which is only possible if all operands to the PHI are
// constants).
Instruction *FoldOpIntoPhi(Instruction &I);
//
// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms
// that would normally be unprofitable because they strongly encourage jump
// threading.
Instruction *FoldOpIntoPhi(Instruction &I, bool AllowAggressive = false);
// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary"
// operator and they all are only used by the PHI, PHI together their
@ -1942,11 +1946,22 @@ static Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
/// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
/// has a PHI node as operand #0, see if we can fold the instruction into the
/// PHI (which is only possible if all operands to the PHI are constants).
Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
///
/// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms
/// that would normally be unprofitable because they strongly encourage jump
/// threading.
Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
bool AllowAggressive) {
AllowAggressive = false;
PHINode *PN = cast<PHINode>(I.getOperand(0));
unsigned NumPHIValues = PN->getNumIncomingValues();
if (!PN->hasOneUse() || NumPHIValues == 0) return 0;
if (NumPHIValues == 0 ||
// We normally only transform phis with a single use, unless we're trying
// hard to make jump threading happen.
(!PN->hasOneUse() && !AllowAggressive))
return 0;
// Check to see if all of the operands of the PHI are simple constants
// (constantint/constantfp/undef). If there is one non-constant value,
// remember the BB it is in. If there is more than one or if *it* is a PHI,
@ -1970,7 +1985,7 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
// operation in that block. However, if this is a critical edge, we would be
// inserting the computation one some other paths (e.g. inside a loop). Only
// do this if the pred block is unconditionally branching into the phi block.
if (NonConstBB) {
if (NonConstBB != 0 && !AllowAggressive) {
BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
if (!BI || !BI->isUnconditional()) return 0;
}
@ -5865,7 +5880,7 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
// block. If in the same block, we're encouraging jump threading. If
// not, we are just pessimizing the code by making an i1 phi.
if (LHSI->getParent() == I.getParent())
if (Instruction *NV = FoldOpIntoPhi(I))
if (Instruction *NV = FoldOpIntoPhi(I, true))
return NV;
break;
case Instruction::SIToFP:
@ -6221,11 +6236,11 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
break;
case Instruction::PHI:
// Only fold icmp into the PHI if the phi and fcmp are in the same
// Only fold icmp into the PHI if the phi and icmp are in the same
// block. If in the same block, we're encouraging jump threading. If
// not, we are just pessimizing the code by making an i1 phi.
if (LHSI->getParent() == I.getParent())
if (Instruction *NV = FoldOpIntoPhi(I))
if (Instruction *NV = FoldOpIntoPhi(I, true))
return NV;
break;
case Instruction::Select: {