From e3868c7d59d4fb551c7159270b99656cc9ea7880 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 7 Oct 2020 18:41:39 -0400 Subject: [PATCH] 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 --- src/backend/parser/gram.y | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y index bc65319c2c..66093b9939 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()