On Jun 19, 2014, at 14:19 , Manuel Klimek <[email protected]> wrote:
> On Thu, Jun 19, 2014 at 6:30 PM, Jordan Rose <[email protected]> wrote: > I think the algorithm makes sense. I'm not sure it's different, though, than > just passing up the first (or last) CXXBindTemporaryExpr visited for a given > expression, which would look like this: > > // For a logical expression... > VisitForTemporaryDtors(E->getLHS(), false, &LastBTE); > const CXXBindTemporaryExpr *InnerBTE = nullptr; > VisitForTemporaryDtors(E->getRHS(), false, &InnerBTE); > InsertTempDtorDecisionBlock(InnerBTE); > > Are there any cases that wouldn't cover? > > Well, the problem is what to do if we don't have a BTE yet; if we only wanted > to pass one pointer, the semantics on function exit would need to be: > if (BTE) { we have already found a BTE, no need to insert a new block when we > encounter the next } > else { we have not yet found a BTE, so we need to insert a new block when we > find one } > > The "unconditional" branch would only fit with the first part, so we would > need to somehow conjure non-null BTE for all unconditional entries, and then > afterwards know that this is a special value, because since we didn't add an > extra block (as we were running an unconditional case), we don't need a > decision block. > I'd say that's a pretty strong argument that we at least need to pass the > CXXBindTemporaryExpr* and a bool IsConditional. > > Now it's right that we don't need to remember the Succ when we hit the > conditional, and instead we could just always store the Succ when we enter a > recursive visitation for a conditional branch (we need to store the Succ > because we can have nested conditionals), but that seems to me like it would > distribute the logic through even more places, and thus undesirable. My observation is that only certain expressions cause conditional branching, and that for these expressions you always need to introduce a new block if you find any destructors, say, in the RHS of a logical expression. So 1. if you're in a non-conditional sub-expression, it doesn't matter whether there are temporaries or not; you don't need to insert a decision branch, 2. if you're in a conditional sub-expression and there are no temporaries, you don't need to insert a decision branch, 3. if you're in a conditional sub-expression and there are temporaries, you can use any temporary from that subexpression as the guard. So it looks to me like the only information you have to pass up from traversing the sub-expressions is a BTE from that subexpression. Everything else can be handled at the point where you start processing that subexpression. What am I missing? Jordan
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