maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[LVI] Add a comment explaining a subtle piece of code 

Or at least, I didn't understand the implications the first several times I read it it.

llvm-svn: 267648
This commit is contained in:
Philip Reames 2016-04-27 01:02:25 +00:00
parent 569a5b38f3
commit 2ab964e263
1 changed files with 23 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
llvm/lib/Analysis/LazyValueInfo.cpp
View File

@ -668,27 +668,35 @@ bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
return true;
}
// If this value is a nonnull pointer, record it's range and bailout.
// If this value is a nonnull pointer, record it's range and bailout. Note
// that for all other pointer typed values, we terminate the search at the
// definition. We could easily extend this to look through geps, bitcasts,
// and the like to prove non-nullness, but it's not clear that's worth it
// compile time wise. The context-insensative value walk done inside
// isKnownNonNull gets most of the profitable cases at much less expense.
// This does mean that we have a sensativity to where the defining
// instruction is placed, even if it could legally be hoisted much higher.
// That is unfortunate.
PointerType *PT = dyn_cast<PointerType>(BBI->getType());
if (PT && isKnownNonNull(BBI)) {
Res = LVILatticeVal::getNot(ConstantPointerNull::get(PT));
insertResult(Val, BB, Res);
return true;
}
if (isa<CastInst>(BBI) && BBI->getType()->isIntegerTy()) {
if (!solveBlockValueCast(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && isa<ConstantInt>(BO->getOperand(1))) {
if (!solveBlockValueBinaryOp(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
else if (BBI->getType()->isIntegerTy()) {
if (isa<CastInst>(BBI)) {
if (!solveBlockValueCast(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && isa<ConstantInt>(BO->getOperand(1))) {
if (!solveBlockValueBinaryOp(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
}
DEBUG(dbgs() << " compute BB '" << BB->getName()