6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2026-04-21 23:17:16 +00:00
Code Issues Projects Releases Wiki Activity

Use LVI to eliminate conditional branches where we've tested a related condition previously. Update tests for this change.

Browse Source 
This fixes PR5652.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112270 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2010-08-27 17:12:29 +00:00
parent 67ef74e0e5
commit 660cab32fe
4 changed files with 53 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Transforms/Scalar/JumpThreading.cpp
+39
View File
@@ -669,6 +669,45 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
}
}
}
// For a comparison where the LHS is outside this block, it's possible
// that we've branch on it before. Used LVI to see if we can simplify
// the branch based on that.
BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
if (LVI && CondBr && CondConst && CondBr->isConditional() &&
(!isa<Instruction>(CondCmp->getOperand(0)) ||
cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
// For predecessor edge, determine if the comparison is true or false
// on that edge. If they're all true or all false, we can simplify the
// branch.
// FIXME: We could handle mixed true/false by duplicating code.
unsigned Trues = 0, Falses = 0, predcount = 0;
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);PI != PE; ++PI){
++predcount;
LazyValueInfo::Tristate Ret =
LVI->getPredicateOnEdge(CondCmp->getPredicate(),
CondCmp->getOperand(0), CondConst, *PI, BB);
if (Ret == LazyValueInfo::True)
++Trues;
else if (Ret == LazyValueInfo::False)
++Falses;
}
// If we can determine the branch direction statically, converted
// the conditional branch to an unconditional one.
if (Trues && Trues == predcount) {
RemovePredecessorAndSimplify(CondBr->getSuccessor(1), BB, TD);
BranchInst::Create(CondBr->getSuccessor(0), CondBr);
CondBr->eraseFromParent();
return true;
} else if (Falses && Falses == predcount) {
RemovePredecessorAndSimplify(CondBr->getSuccessor(0), BB, TD);
BranchInst::Create(CondBr->getSuccessor(1), CondBr);
CondBr->eraseFromParent();
return true;
}
}
}
// Check for some cases that are worth simplifying. Right now we want to look