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 ae800d565fa55402d2fbd231b8ac58e51b06a53e..6e15df231fae06c6192985ad9157d746dfc7a474 100644 (file)
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -14533,7 +14533,7 @@ 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)
@@ -14557,10 +14557,10 @@ 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()