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authorTom Lane <tgl@sss.pgh.pa.us>2020-10-07 18:41:39 -0400
committerTom Lane <tgl@sss.pgh.pa.us>2020-10-07 18:42:23 -0400
commite3868c7d59d4fb551c7159270b99656cc9ea7880 (patch)
tree9d2f0613b68495fcd027fde0d6b58e8aa5c71495
parentf2c6e94f07908104942920efd57c55413d32a84a (diff)
downloadpostgresql-e3868c7d59d4fb551c7159270b99656cc9ea7880.tar.gz
postgresql-e3868c7d59d4fb551c7159270b99656cc9ea7880.zip
Fix optimization hazard in gram.y's makeOrderedSetArgs(), redux.
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
-rw-r--r--src/backend/parser/gram.y6
1 files changed, 3 insertions, 3 deletions
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index bc65319c2c4..66093b9939d 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -15812,7 +15812,7 @@ makeOrderedSetArgs(List *directargs, List *orderedargs,
core_yyscan_t yyscanner)
{
FunctionParameter *lastd = (FunctionParameter *) llast(directargs);
- int ndirectargs;
+ Value *ndirectargs;
/* No restriction unless last direct arg is VARIADIC */
if (lastd->mode == FUNC_PARAM_VARIADIC)
@@ -15836,10 +15836,10 @@ makeOrderedSetArgs(List *directargs, List *orderedargs,
}
/* 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),
- makeInteger(ndirectargs));
+ ndirectargs);
}
/* insertSelectOptions()