Add repalloc0 and repalloc0_array

These zero out the space added by repalloc.  This is a common pattern
that is quite hairy to code by hand.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/b66dfc89-9365-cb57-4e1f-b7d31813eeec@enterprisedb.com

src/backend/executor/nodeHash.c

@@ -940,12 +940,8 @@ ExecHashIncreaseNumBatches(HashJoinTable hashtable)
 	else
 	{
 		/* enlarge arrays and zero out added entries */
-		hashtable->innerBatchFile = repalloc_array(hashtable->innerBatchFile, BufFile *, nbatch);
-		hashtable->outerBatchFile = repalloc_array(hashtable->outerBatchFile, BufFile *, nbatch);
-		MemSet(hashtable->innerBatchFile + oldnbatch, 0,
-			   (nbatch - oldnbatch) * sizeof(BufFile *));
-		MemSet(hashtable->outerBatchFile + oldnbatch, 0,
-			   (nbatch - oldnbatch) * sizeof(BufFile *));
+		hashtable->innerBatchFile = repalloc0_array(hashtable->innerBatchFile, BufFile *, oldnbatch, nbatch);
+		hashtable->outerBatchFile = repalloc0_array(hashtable->outerBatchFile, BufFile *, oldnbatch, nbatch);
 	}
 
 	MemoryContextSwitchTo(oldcxt);

src/backend/libpq/be-fsstubs.c

@@ -696,19 +696,16 @@ newLOfd(void)
 		newsize = 64;
 		cookies = (LargeObjectDesc **)
 			MemoryContextAllocZero(fscxt, newsize * sizeof(LargeObjectDesc *));
-		cookies_size = newsize;
 	}
 	else
 	{
 		/* Double size of array */
 		i = cookies_size;
 		newsize = cookies_size * 2;
-		cookies = (LargeObjectDesc **)
-			repalloc(cookies, newsize * sizeof(LargeObjectDesc *));
-		MemSet(cookies + cookies_size, 0,
-			   (newsize - cookies_size) * sizeof(LargeObjectDesc *));
-		cookies_size = newsize;
+		cookies =
+			repalloc0_array(cookies, LargeObjectDesc *, cookies_size, newsize);
 	}
+	cookies_size = newsize;
 
 	return i;
 }

src/backend/optimizer/util/placeholder.c

@@ -133,16 +133,11 @@ find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
 		while (phinfo->phid >= new_size)
 			new_size *= 2;
 		if (root->placeholder_array)
-		{
-			root->placeholder_array = (PlaceHolderInfo **)
-				repalloc(root->placeholder_array,
-						 sizeof(PlaceHolderInfo *) * new_size);
-			MemSet(root->placeholder_array + root->placeholder_array_size, 0,
-				   sizeof(PlaceHolderInfo *) * (new_size - root->placeholder_array_size));
-		}
+			root->placeholder_array =
+				repalloc0_array(root->placeholder_array, PlaceHolderInfo *, root->placeholder_array_size, new_size);
 		else
-			root->placeholder_array = (PlaceHolderInfo **)
-				palloc0(new_size * sizeof(PlaceHolderInfo *));
+			root->placeholder_array =
+				palloc0_array(PlaceHolderInfo *, new_size);
 		root->placeholder_array_size = new_size;
 	}
 	root->placeholder_array[phinfo->phid] = phinfo;

src/backend/optimizer/util/relnode.c

@@ -157,31 +157,18 @@ expand_planner_arrays(PlannerInfo *root, int add_size)
 
 	new_size = root->simple_rel_array_size + add_size;
 
-	root->simple_rel_array = (RelOptInfo **)
-		repalloc(root->simple_rel_array,
-				 sizeof(RelOptInfo *) * new_size);
-	MemSet(root->simple_rel_array + root->simple_rel_array_size,
-		   0, sizeof(RelOptInfo *) * add_size);
+	root->simple_rel_array =
+		repalloc0_array(root->simple_rel_array, RelOptInfo *, root->simple_rel_array_size, new_size);
 
-	root->simple_rte_array = (RangeTblEntry **)
-		repalloc(root->simple_rte_array,
-				 sizeof(RangeTblEntry *) * new_size);
-	MemSet(root->simple_rte_array + root->simple_rel_array_size,
-		   0, sizeof(RangeTblEntry *) * add_size);
+	root->simple_rte_array =
+		repalloc0_array(root->simple_rte_array, RangeTblEntry *, root->simple_rel_array_size, new_size);
 
 	if (root->append_rel_array)
-	{
-		root->append_rel_array = (AppendRelInfo **)
-			repalloc(root->append_rel_array,
-					 sizeof(AppendRelInfo *) * new_size);
-		MemSet(root->append_rel_array + root->simple_rel_array_size,
-			   0, sizeof(AppendRelInfo *) * add_size);
-	}
+		root->append_rel_array =
+			repalloc0_array(root->append_rel_array, AppendRelInfo *, root->simple_rel_array_size, new_size);
 	else
-	{
-		root->append_rel_array = (AppendRelInfo **)
-			palloc0(sizeof(AppendRelInfo *) * new_size);
-	}
+		root->append_rel_array =
+			palloc0_array(AppendRelInfo *, new_size);
 
 	root->simple_rel_array_size = new_size;
 }

src/backend/parser/parse_param.c

@@ -145,14 +145,10 @@ variable_paramref_hook(ParseState *pstate, ParamRef *pref)
 	{
 		/* Need to enlarge param array */
 		if (*parstate->paramTypes)
-			*parstate->paramTypes = (Oid *) repalloc(*parstate->paramTypes,
-													 paramno * sizeof(Oid));
+			*parstate->paramTypes = repalloc0_array(*parstate->paramTypes, Oid,
+													*parstate->numParams, paramno);
 		else
-			*parstate->paramTypes = (Oid *) palloc(paramno * sizeof(Oid));
-		/* Zero out the previously-unreferenced slots */
-		MemSet(*parstate->paramTypes + *parstate->numParams,
-			   0,
-			   (paramno - *parstate->numParams) * sizeof(Oid));
+			*parstate->paramTypes = palloc0_array(Oid, paramno);
 		*parstate->numParams = paramno;
 	}
 

src/backend/storage/lmgr/lwlock.c

@@ -668,13 +668,8 @@ LWLockRegisterTranche(int tranche_id, const char *tranche_name)
 				MemoryContextAllocZero(TopMemoryContext,
 									   newalloc * sizeof(char *));
 		else
-		{
-			LWLockTrancheNames = (const char **)
-				repalloc(LWLockTrancheNames, newalloc * sizeof(char *));
-			memset(LWLockTrancheNames + LWLockTrancheNamesAllocated,
-				   0,
-				   (newalloc - LWLockTrancheNamesAllocated) * sizeof(char *));
-		}
+			LWLockTrancheNames =
+				repalloc0_array(LWLockTrancheNames, const char *, LWLockTrancheNamesAllocated, newalloc);
 		LWLockTrancheNamesAllocated = newalloc;
 	}
 

src/backend/utils/adt/ruleutils.c

@@ -4855,14 +4855,9 @@ expand_colnames_array_to(deparse_columns *colinfo, int n)
 	if (n > colinfo->num_cols)
 	{
 		if (colinfo->colnames == NULL)
-			colinfo->colnames = (char **) palloc0(n * sizeof(char *));
+			colinfo->colnames = palloc0_array(char *, n);
 		else
-		{
-			colinfo->colnames = (char **) repalloc(colinfo->colnames,
-												   n * sizeof(char *));
-			memset(colinfo->colnames + colinfo->num_cols, 0,
-				   (n - colinfo->num_cols) * sizeof(char *));
-		}
+			colinfo->colnames = repalloc0_array(colinfo->colnames, char *, colinfo->num_cols, n);
 		colinfo->num_cols = n;
 	}
 }

src/backend/utils/cache/typcache.c

@@ -1714,14 +1714,8 @@ ensure_record_cache_typmod_slot_exists(int32 typmod)
 	{
 		int32		newlen = pg_nextpower2_32(typmod + 1);
 
-		RecordCacheArray = (TupleDesc *) repalloc(RecordCacheArray,
-												  newlen * sizeof(TupleDesc));
-		memset(RecordCacheArray + RecordCacheArrayLen, 0,
-			   (newlen - RecordCacheArrayLen) * sizeof(TupleDesc));
-		RecordIdentifierArray = (uint64 *) repalloc(RecordIdentifierArray,
-													newlen * sizeof(uint64));
-		memset(RecordIdentifierArray + RecordCacheArrayLen, 0,
-			   (newlen - RecordCacheArrayLen) * sizeof(uint64));
+		RecordCacheArray = repalloc0_array(RecordCacheArray, TupleDesc, RecordCacheArrayLen, newlen);
+		RecordIdentifierArray = repalloc0_array(RecordIdentifierArray, uint64, RecordCacheArrayLen, newlen);
 		RecordCacheArrayLen = newlen;
 	}
 }

src/backend/utils/mmgr/mcxt.c

@@ -1395,6 +1395,26 @@ repalloc_extended(void *pointer, Size size, int flags)
 	return ret;
 }
 
+/*
+ * repalloc0
+ *		Adjust the size of a previously allocated chunk and zero out the added
+ *		space.
+ */
+void *
+repalloc0(void *pointer, Size oldsize, Size size)
+{
+	void	   *ret;
+
+	/* catch wrong argument order */
+	if (unlikely(oldsize > size))
+		elog(ERROR, "invalid repalloc0 call: oldsize %zu, new size %zu",
+			 oldsize, size);
+
+	ret = repalloc(pointer, size);
+	memset((char *) ret + oldsize, 0, (size - oldsize));
+	return ret;
+}
+
 /*
  * MemoryContextAllocHuge
  *		Allocate (possibly-expansive) space within the specified context.

src/include/utils/palloc.h

@@ -80,6 +80,7 @@ extern void *palloc_extended(Size size, int flags);
 extern pg_nodiscard void *repalloc(void *pointer, Size size);
 extern pg_nodiscard void *repalloc_extended(void *pointer,
 											Size size, int flags);
+extern pg_nodiscard void *repalloc0(void *pointer, Size oldsize, Size size);
 extern void pfree(void *pointer);
 
 /*
@@ -103,6 +104,7 @@ extern void pfree(void *pointer);
  * objects of type "type"
  */
 #define repalloc_array(pointer, type, count) ((type *) repalloc(pointer, sizeof(type) * (count)))
+#define repalloc0_array(pointer, type, oldcount, count) ((type *) repalloc0(pointer, sizeof(type) * (oldcount), sizeof(type) * (count)))
 
 /*
  * The result of palloc() is always word-aligned, so we can skip testing