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

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 53773a9e99a78c7e126e2608d2aeb8cb92f9e9cc..e31a8181d122952956783a986bfac1da482cdc14 100644 (file)
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -15409,7 +15409,7 @@ 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)
@@ -15433,10 +15433,10 @@ 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()