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Fix optimization hazard in gram.y's makeOrderedSetArgs(), redux.

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It appears that commit cf63c641c, which intended to prevent
misoptimization of the result-building step in makeOrderedSetArgs,
didn't go far enough: buildfarm member hornet's version of xlc
is now optimizing back to the old, broken behavior in which
list_length(directargs) is fetched only after list_concat() has
changed that value.  I'm not entirely convinced whether that's
an undeniable compiler bug or whether it can be justified by a
sufficiently aggressive interpretation of C sequence points.
So let's just change the code to make it harder to misinterpret.

Back-patch to all supported versions, just in case.

Discussion: https://postgr.es/m/1830491.1601944935@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2020-10-07 18:41:39 -04:00
parent 0c79dcb36c
commit 9f3d3fb870
1 changed files with 3 additions and 3 deletions
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6
src/backend/parser/gram.y
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@ -15409,7 +15409,7 @@ makeOrderedSetArgs(List *directargs, List *orderedargs,
core_yyscan_t yyscanner) core_yyscan_t yyscanner)
{ {
FunctionParameter *lastd = (FunctionParameter *) llast(directargs); FunctionParameter *lastd = (FunctionParameter *) llast(directargs);
int ndirectargs; Value *ndirectargs;
/* No restriction unless last direct arg is VARIADIC */ /* No restriction unless last direct arg is VARIADIC */
if (lastd->mode == FUNC_PARAM_VARIADIC) if (lastd->mode == FUNC_PARAM_VARIADIC)
@ -15433,10 +15433,10 @@ makeOrderedSetArgs(List *directargs, List *orderedargs,
} }
/* don't merge into the next line, as list_concat changes directargs */ /* don't merge into the next line, as list_concat changes directargs */
ndirectargs = list_length(directargs); ndirectargs = makeInteger(list_length(directargs));
return list_make2(list_concat(directargs, orderedargs), return list_make2(list_concat(directargs, orderedargs),
makeInteger(ndirectargs)); ndirectargs);
} }
/* insertSelectOptions() /* insertSelectOptions()