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IndVarSimplify: do not recompute an IV value outside of the loop if :

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- it is trivially known to be used inside the loop in a way that can not be optimized away
- there is no use outside of the loop which can take advantage of the computation hoisting

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177432 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnaud A. de Grandmaison
2013-03-19 20:00:22 +00:00
parent dff4d1522a
commit eb9a42e8ab
2 changed files with 108 additions and 0 deletions
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39
lib/Transforms/Scalar/IndVarSimplify.cpp
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@@ -535,6 +535,45 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
if (!SE->isLoopInvariant(ExitValue, L))
continue;
// Computing the value outside of the loop brings no benefit if :
// - it is definitely used inside the loop in a way which can not be
// optimized away.
// - no use outside of the loop can take advantage of hoisting the
// computation out of the loop
if (ExitValue->getSCEVType()>=scMulExpr) {
unsigned NumHardInternalUses = 0;
unsigned NumSoftExternalUses = 0;
unsigned NumUses = 0;
for (Value::use_iterator IB=Inst->use_begin(), IE=Inst->use_end();
IB!=IE && NumUses<=6 ; ++IB) {
Instruction *UseInstr = cast<Instruction>(*IB);
unsigned Opc = UseInstr->getOpcode();
NumUses++;
if (L->contains(UseInstr)) {
if (Opc == Instruction::Call || Opc == Instruction::Ret)
NumHardInternalUses++;
} else {
if (Opc == Instruction::PHI) {
// Do not count the Phi as a use. LCSSA may have inserted
// plenty of trivial ones.
NumUses--;
for (Value::use_iterator PB=UseInstr->use_begin(),
PE=UseInstr->use_end();
PB!=PE && NumUses<=6 ; ++PB, ++NumUses) {
unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret)
NumSoftExternalUses++;
}
continue;
}
if (Opc != Instruction::Call && Opc != Instruction::Ret)
NumSoftExternalUses++;
}
}
if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses)
continue;
}
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'