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

It appears that commitcf63c64, which intended to preventmisoptimization of the result-building step in makeOrderedSetArgs,didn't go far enough: buildfarm member hornet's version of xlcis now optimizing back to the old, broken behavior in whichlist_length(directargs) is fetched only after list_concat() haschanged that value. I'm not entirely convinced whether that'san undeniable compiler bug or whether it can be justified by asufficiently 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

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src/backend/parser
- gram.y

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`‎src/backend/parser/gram.y`

Lines changed: 3 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -15817,7 +15817,7 @@ makeOrderedSetArgs(List directargs, List orderedargs,`
`15817`	`15817`	`core_yyscan_t yyscanner)`
`15818`	`15818`	`{`
`15819`	`15819`	`FunctionParameter lastd = (FunctionParameter ) llast(directargs);`
`15820`		`-intndirectargs;`
	`15820`	`+Value *ndirectargs;`
`15821`	`15821`
`15822`	`15822`	`/* No restriction unless last direct arg is VARIADIC*/`
`15823`	`15823`	`if (lastd->mode == FUNC_PARAM_VARIADIC)`
`@@ -15841,10 +15841,10 @@ makeOrderedSetArgs(List directargs, List orderedargs,`
`15841`	`15841`	`}`
`15842`	`15842`
`15843`	`15843`	`/* don't merge into the next line, as list_concat changes directargs*/`
`15844`		`-ndirectargs = list_length(directargs);`
	`15844`	`+ndirectargs =makeInteger(list_length(directargs));`
`15845`	`15845`
`15846`	`15846`	`return list_make2(list_concat(directargs, orderedargs),`
`15847`		`-makeInteger(ndirectargs));`
	`15847`	`+ ndirectargs);`
`15848`	`15848`	`}`
`15849`	`15849`
`15850`	`15850`	`/* insertSelectOptions()`

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Commit8b231d9

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`‎src/backend/parser/gram.y`

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