[TempRValueOpt] Fold added destroy_addrs into loads/copy_addrs. #65052
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nate-chandler
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eeckstein
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Apr 11, 2023
| li->getOwnershipQualifier() != LoadOwnershipQualifier::Take; | ||
| } | ||
| return true; | ||
| }(); |
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Maybe you can add an assert here to check if it's a move only type then needToInsertDestroy must be false
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Added asserts along those lines in 1021519 . (Along with a test illustrating why needToInsertDestroy might be true even when the type is move-only--if lastLoadInst is an apply.)
In preparation for "folding" an "inserted destroy" into a load [copy] or copy_addr, rename the variable that indicates whether the copyInst's source must be deinitialized after its last "load".
As a separate commit to make the behavior change more obvious.
To avoid introducing new copies--which is illegal for move-only values-- don't rewrite `load [take]`s and `copy_addr [take]`s as `load [copy]`s and `copy_addr`s respectively and introduce new `destroy_addr`s after them. Instead, get the effect of folding such a newly created `destroy_addr` into the preceding rewritten `load [copy]` or `copy_addr`. Get that effect by neither modifying the `copy_addr [take]` or `load [take]` nor adding a subsequent `destroy_addr`. An example for each kind (`load [take]` and `copy_addr [take]`): ``` // Input 1 (`load [take]`) copy_addr [take] %src to [init] %tmp %val = load [take] %src // Old Output 1 %val = load [copy] %src destroy_addr %src // New Output 2 %val = load [take] %src ``` ``` // Input 2 (`copy_addr [take]`) copy_addr [take] %src to [init] %tmp copy_addr [take] %src to [init] %dst // Old Output 2 copy_addr %src to [init] %dst destroy_addr %src // New Output 2 copy_addr [take] %src to [init] %dst ``` rdar://107839979
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eeckstein
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| if (lastLoadInst == copyInst) | ||
| return true; | ||
| if (auto *cai = dyn_cast<CopyAddrInst>(lastLoadInst)) { | ||
| auto retval = cai->getSrc() != tempObj || !cai->isTakeOfSrc(); |
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nitpick: all these conditions are getting hard to understand. IMO, for clarity it's better to write
if (cai->getSrc() == tempObj && cai->isTakeOfSrc()) {
// Can reuse the last copy_addr as deinitialization.
return false;
} else {
assert(!tempObj->getType().isMoveOnly() && "introducing copy of move-only value!?");
return true;
}
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To avoid introducing new copies--which is illegal for move-only values-- don't rewrite
load [take]s andcopy_addr [take]s asload [copy]s andcopy_addrs respectively and introduce newdestroy_addrs after them. Instead, get the effect of folding such a newly createddestroy_addrinto the preceding rewrittenload [copy]orcopy_addr. Get that effect by neither modifying thecopy_addr [take]orload [take]nor adding a subsequentdestroy_addr.An example for each kind (
load [take]andcopy_addr [take]):rdar://107839979