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Commit2072932

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committed
Suppress unnecessary RelabelType nodes in yet more cases.
Commita477bfc fixed eval_const_expressions() to ensure that itdidn't generate unnecessary RelabelType nodes, but I failed to noticethat some other places in the planner had the same issue. Reallynoplace in the planner should be using plain makeRelabelType(), forfear of generating expressions that should be equal() to semanticallyequivalent trees, but aren't.An example is that because canonicalize_ec_expression() failedto be careful about this, we could end up with an equivalence classcontaining both a plain Const, and a Const-with-RelabelTyperepresenting exactly the same value. So far as I can tell this led tono visible misbehavior, but we did waste a bunch of cycles generatingand evaluating "Const = Const-with-RelabelType" to prove such entriesare redundant.Hence, move the support function added bya477bfc to where it canbe more generally useful, and use it in the places where planner codepreviously used makeRelabelType.Back-patch to v12, like the previous patch. While I have no concreteevidence of any real misbehavior here, it's certainly possible thatI overlooked a case where equivalent expressions that aren't equal()could cause a user-visible problem. In any case carrying extraRelabelType nodes through planning to execution isn't very desirable.Discussion:https://postgr.es/m/1311836.1597781384@sss.pgh.pa.us
1 parent3e98c0b commit2072932

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5 files changed

+106
-119
lines changed

5 files changed

+106
-119
lines changed

‎src/backend/nodes/nodeFuncs.c

Lines changed: 62 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -575,27 +575,76 @@ exprIsLengthCoercion(const Node *expr, int32 *coercedTypmod)
575575
return false;
576576
}
577577

578+
/*
579+
* applyRelabelType
580+
*Add a RelabelType node if needed to make the expression expose
581+
*the specified type, typmod, and collation.
582+
*
583+
* This is primarily intended to be used during planning. Therefore, it must
584+
* maintain the post-eval_const_expressions invariants that there are not
585+
* adjacent RelabelTypes, and that the tree is fully const-folded (hence,
586+
* we mustn't return a RelabelType atop a Const). If we do find a Const,
587+
* we'll modify it in-place if "overwrite_ok" is true; that should only be
588+
* passed as true if caller knows the Const is newly generated.
589+
*/
590+
Node*
591+
applyRelabelType(Node*arg,Oidrtype,int32rtypmod,Oidrcollid,
592+
CoercionFormrformat,intrlocation,booloverwrite_ok)
593+
{
594+
/*
595+
* If we find stacked RelabelTypes (eg, from foo::int::oid) we can discard
596+
* all but the top one, and must do so to ensure that semantically
597+
* equivalent expressions are equal().
598+
*/
599+
while (arg&&IsA(arg,RelabelType))
600+
arg= (Node*) ((RelabelType*)arg)->arg;
601+
602+
if (arg&&IsA(arg,Const))
603+
{
604+
/* Modify the Const directly to preserve const-flatness. */
605+
Const*con= (Const*)arg;
606+
607+
if (!overwrite_ok)
608+
con=copyObject(con);
609+
con->consttype=rtype;
610+
con->consttypmod=rtypmod;
611+
con->constcollid=rcollid;
612+
/* We keep the Const's original location. */
613+
return (Node*)con;
614+
}
615+
elseif (exprType(arg)==rtype&&
616+
exprTypmod(arg)==rtypmod&&
617+
exprCollation(arg)==rcollid)
618+
{
619+
/* Sometimes we find a nest of relabels that net out to nothing. */
620+
returnarg;
621+
}
622+
else
623+
{
624+
/* Nope, gotta have a RelabelType. */
625+
RelabelType*newrelabel=makeNode(RelabelType);
626+
627+
newrelabel->arg= (Expr*)arg;
628+
newrelabel->resulttype=rtype;
629+
newrelabel->resulttypmod=rtypmod;
630+
newrelabel->resultcollid=rcollid;
631+
newrelabel->relabelformat=rformat;
632+
newrelabel->location=rlocation;
633+
return (Node*)newrelabel;
634+
}
635+
}
636+
578637
/*
579638
* relabel_to_typmod
580639
*Add a RelabelType node that changes just the typmod of the expression.
581640
*
582-
* This is primarily intended to be used during planning. Therefore, it
583-
* strips any existing RelabelType nodes to maintain the planner's invariant
584-
* that there are not adjacent RelabelTypes.
641+
* Convenience function for a common usage of applyRelabelType.
585642
*/
586643
Node*
587644
relabel_to_typmod(Node*expr,int32typmod)
588645
{
589-
Oidtype=exprType(expr);
590-
Oidcoll=exprCollation(expr);
591-
592-
/* Strip any existing RelabelType node(s) */
593-
while (expr&&IsA(expr,RelabelType))
594-
expr= (Node*) ((RelabelType*)expr)->arg;
595-
596-
/* Apply new typmod, preserving the previous exposed type and collation */
597-
return (Node*)makeRelabelType((Expr*)expr,type,typmod,coll,
598-
COERCE_EXPLICIT_CAST);
646+
returnapplyRelabelType(expr,exprType(expr),typmod,exprCollation(expr),
647+
COERCE_EXPLICIT_CAST,-1, false);
599648
}
600649

601650
/*

‎src/backend/optimizer/path/equivclass.c

Lines changed: 17 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -490,10 +490,6 @@ process_equivalence(PlannerInfo *root,
490490
* work to not label the collation at all in EC members, but this is risky
491491
* since some parts of the system expect exprCollation() to deliver the
492492
* right answer for a sort key.)
493-
*
494-
* Note this code assumes that the expression has already been through
495-
* eval_const_expressions, so there are no CollateExprs and no redundant
496-
* RelabelTypes.
497493
*/
498494
Expr*
499495
canonicalize_ec_expression(Expr*expr,Oidreq_type,Oidreq_collation)
@@ -514,29 +510,24 @@ canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
514510
exprCollation((Node*)expr)!=req_collation)
515511
{
516512
/*
517-
* Strip any existing RelabelType, then add a new one if needed. This
518-
* is to preserve the invariant of no redundant RelabelTypes.
519-
*
520-
* If we have to change the exposed type of the stripped expression,
521-
* set typmod to -1 (since the new type may not have the same typmod
522-
* interpretation). If we only have to change collation, preserve the
523-
* exposed typmod.
513+
* If we have to change the type of the expression, set typmod to -1,
514+
* since the new type may not have the same typmod interpretation.
515+
* When we only have to change collation, preserve the exposed typmod.
516+
*/
517+
int32req_typmod;
518+
519+
if (expr_type!=req_type)
520+
req_typmod=-1;
521+
else
522+
req_typmod=exprTypmod((Node*)expr);
523+
524+
/*
525+
* Use applyRelabelType so that we preserve const-flatness. This is
526+
* important since eval_const_expressions has already been applied.
524527
*/
525-
while (expr&&IsA(expr,RelabelType))
526-
expr= (Expr*) ((RelabelType*)expr)->arg;
527-
528-
if (exprType((Node*)expr)!=req_type)
529-
expr= (Expr*)makeRelabelType(expr,
530-
req_type,
531-
-1,
532-
req_collation,
533-
COERCE_IMPLICIT_CAST);
534-
elseif (exprCollation((Node*)expr)!=req_collation)
535-
expr= (Expr*)makeRelabelType(expr,
536-
req_type,
537-
exprTypmod((Node*)expr),
538-
req_collation,
539-
COERCE_IMPLICIT_CAST);
528+
expr= (Expr*)applyRelabelType((Node*)expr,
529+
req_type,req_typmod,req_collation,
530+
COERCE_IMPLICIT_CAST,-1, false);
540531
}
541532

542533
returnexpr;

‎src/backend/optimizer/prep/prepunion.c

Lines changed: 3 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1200,13 +1200,9 @@ generate_setop_tlist(List *colTypes, List *colCollations,
12001200
* will reach the executor without any further processing.
12011201
*/
12021202
if (exprCollation(expr)!=colColl)
1203-
{
1204-
expr= (Node*)makeRelabelType((Expr*)expr,
1205-
exprType(expr),
1206-
exprTypmod(expr),
1207-
colColl,
1208-
COERCE_IMPLICIT_CAST);
1209-
}
1203+
expr=applyRelabelType(expr,
1204+
exprType(expr),exprTypmod(expr),colColl,
1205+
COERCE_IMPLICIT_CAST,-1, false);
12101206

12111207
tle=makeTargetEntry((Expr*)expr,
12121208
(AttrNumber)resno++,

‎src/backend/optimizer/util/clauses.c

Lines changed: 21 additions & 73 deletions
Original file line numberDiff line numberDiff line change
@@ -120,9 +120,6 @@ static Node *eval_const_expressions_mutator(Node *node,
120120
staticboolcontain_non_const_walker(Node*node,void*context);
121121
staticboolece_function_is_safe(Oidfuncid,
122122
eval_const_expressions_context*context);
123-
staticNode*apply_const_relabel(Node*arg,Oidrtype,
124-
int32rtypmod,Oidrcollid,
125-
CoercionFormrformat,intrlocation);
126123
staticList*simplify_or_arguments(List*args,
127124
eval_const_expressions_context*context,
128125
bool*haveNull,bool*forceTrue);
@@ -2819,12 +2816,13 @@ eval_const_expressions_mutator(Node *node,
28192816
arg=eval_const_expressions_mutator((Node*)relabel->arg,
28202817
context);
28212818
/* ... and attach a new RelabelType node, if needed */
2822-
returnapply_const_relabel(arg,
2823-
relabel->resulttype,
2824-
relabel->resulttypmod,
2825-
relabel->resultcollid,
2826-
relabel->relabelformat,
2827-
relabel->location);
2819+
returnapplyRelabelType(arg,
2820+
relabel->resulttype,
2821+
relabel->resulttypmod,
2822+
relabel->resultcollid,
2823+
relabel->relabelformat,
2824+
relabel->location,
2825+
true);
28282826
}
28292827
caseT_CoerceViaIO:
28302828
{
@@ -2971,12 +2969,13 @@ eval_const_expressions_mutator(Node *node,
29712969
arg=eval_const_expressions_mutator((Node*)collate->arg,
29722970
context);
29732971
/* ... and attach a new RelabelType node, if needed */
2974-
returnapply_const_relabel(arg,
2975-
exprType(arg),
2976-
exprTypmod(arg),
2977-
collate->collOid,
2978-
COERCE_IMPLICIT_CAST,
2979-
collate->location);
2972+
returnapplyRelabelType(arg,
2973+
exprType(arg),
2974+
exprTypmod(arg),
2975+
collate->collOid,
2976+
COERCE_IMPLICIT_CAST,
2977+
collate->location,
2978+
true);
29802979
}
29812980
caseT_CaseExpr:
29822981
{
@@ -3478,12 +3477,13 @@ eval_const_expressions_mutator(Node *node,
34783477
cdomain->resulttype);
34793478

34803479
/* Generate RelabelType to substitute for CoerceToDomain */
3481-
returnapply_const_relabel(arg,
3482-
cdomain->resulttype,
3483-
cdomain->resulttypmod,
3484-
cdomain->resultcollid,
3485-
cdomain->coercionformat,
3486-
cdomain->location);
3480+
returnapplyRelabelType(arg,
3481+
cdomain->resulttype,
3482+
cdomain->resulttypmod,
3483+
cdomain->resultcollid,
3484+
cdomain->coercionformat,
3485+
cdomain->location,
3486+
true);
34873487
}
34883488

34893489
newcdomain=makeNode(CoerceToDomain);
@@ -3616,58 +3616,6 @@ ece_function_is_safe(Oid funcid, eval_const_expressions_context *context)
36163616
return false;
36173617
}
36183618

3619-
/*
3620-
* Subroutine for eval_const_expressions: apply RelabelType if needed
3621-
*/
3622-
staticNode*
3623-
apply_const_relabel(Node*arg,Oidrtype,int32rtypmod,Oidrcollid,
3624-
CoercionFormrformat,intrlocation)
3625-
{
3626-
/*
3627-
* If we find stacked RelabelTypes (eg, from foo::int::oid) we can discard
3628-
* all but the top one, and must do so to ensure that semantically
3629-
* equivalent expressions are equal().
3630-
*/
3631-
while (arg&&IsA(arg,RelabelType))
3632-
arg= (Node*) ((RelabelType*)arg)->arg;
3633-
3634-
if (arg&&IsA(arg,Const))
3635-
{
3636-
/*
3637-
* If it's a Const, just modify it in-place; since this is part of
3638-
* eval_const_expressions, we want to end up with a simple Const not
3639-
* an expression tree. We assume the Const is newly generated and
3640-
* hence safe to modify.
3641-
*/
3642-
Const*con= (Const*)arg;
3643-
3644-
con->consttype=rtype;
3645-
con->consttypmod=rtypmod;
3646-
con->constcollid=rcollid;
3647-
return (Node*)con;
3648-
}
3649-
elseif (exprType(arg)==rtype&&
3650-
exprTypmod(arg)==rtypmod&&
3651-
exprCollation(arg)==rcollid)
3652-
{
3653-
/* Sometimes we find a nest of relabels that net out to nothing. */
3654-
returnarg;
3655-
}
3656-
else
3657-
{
3658-
/* Nope, gotta have a RelabelType. */
3659-
RelabelType*newrelabel=makeNode(RelabelType);
3660-
3661-
newrelabel->arg= (Expr*)arg;
3662-
newrelabel->resulttype=rtype;
3663-
newrelabel->resulttypmod=rtypmod;
3664-
newrelabel->resultcollid=rcollid;
3665-
newrelabel->relabelformat=rformat;
3666-
newrelabel->location=rlocation;
3667-
return (Node*)newrelabel;
3668-
}
3669-
}
3670-
36713619
/*
36723620
* Subroutine for eval_const_expressions: process arguments of an OR clause
36733621
*

‎src/include/nodes/nodeFuncs.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,6 +36,9 @@ typedef bool (*check_function_callback) (Oid func_id, void *context);
3636
externOidexprType(constNode*expr);
3737
externint32exprTypmod(constNode*expr);
3838
externboolexprIsLengthCoercion(constNode*expr,int32*coercedTypmod);
39+
externNode*applyRelabelType(Node*arg,Oidrtype,int32rtypmod,Oidrcollid,
40+
CoercionFormrformat,intrlocation,
41+
booloverwrite_ok);
3942
externNode*relabel_to_typmod(Node*expr,int32typmod);
4043
externNode*strip_implicit_coercions(Node*node);
4144
externboolexpression_returns_set(Node*clause);

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