Commit677f74e

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Avoid memcpy() with a NULL source pointer and count == 0

When memcpy() is called on a pointer, the compiler is entitled to assumethat the pointer is not null, which can lead to optimizing nearby codein potentially undesirable ways. We still want such optimizations(gcc's -fdelete-null-pointer-checks) in cases where they're valid.Related: commit13bba02.Backpatch to pg11, where this particular instance appeared.Reported-by: Ranier Vilela <ranier.vf@gmail.com>Reported-by: Zhihong Yu <zyu@yugabyte.com>Discussion:https://postgr.es/m/CAEudQApUndmQkr5fLrCKXQ7+ib44i7S+Kk93pyVThS85PnG3bQ@mail.gmail.comDiscussion:https://postgr.es/m/CALNJ-vSdhwSM5f4tnNn1cdLHvXMVe_S+V3nR5GwNrmCPNB2VtQ@mail.gmail.com

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Original file line number	Diff line number	Diff line change
`@@ -1163,15 +1163,17 @@ DefineIndex(Oid relationId,`
`1163`	`1163`
`1164`	`1164`	`if (partitioned)`
`1165`	`1165`	`{`
	`1166`	`+PartitionDescpartdesc;`
	`1167`	`+`
`1166`	`1168`	`/*`
`1167`	`1169`	`* Unless caller specified to skip this step (via ONLY), process each`
`1168`	`1170`	`* partition to make sure they all contain a corresponding index.`
`1169`	`1171`	`*`
`1170`	`1172`	`* If we're called internally (no stmt->relation), recurse always.`
`1171`	`1173`	`*/`
`1172`		`-if (!stmt->relation\|\|stmt->relation->inh)`
	`1174`	`+partdesc=RelationGetPartitionDesc(rel);`
	`1175`	`+if ((!stmt->relation\|\|stmt->relation->inh)&&partdesc->nparts>0)`
`1173`	`1176`	`{`
`1174`		`-PartitionDescpartdesc=RelationGetPartitionDesc(rel);`
`1175`	`1177`	`intnparts=partdesc->nparts;`
`1176`	`1178`	`Oidpart_oids=palloc(sizeof(Oid)nparts);`
`1177`	`1179`	`boolinvalidate_parent= false;`

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