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Commit136ab7c

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Marginal improvement for generated code in execExprInterp.c.
Avoid the coding pattern "*op->resvalue = f();", as some compilers thinkthat requires them to evaluate "op->resvalue" before the function call.Unless there are lots of free registers, this can lead to a uselessregister spill and reload across the call.I changed all the cases like this in ExecInterpExpr(), but didn't botherin the out-of-line opcode eval subroutines, since those are presumablynot as performance-critical.Discussion:https://postgr.es/m/2508.1506630094@sss.pgh.pa.us
1 parent5373bc2 commit136ab7c

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1 file changed

+42
-17
lines changed

1 file changed

+42
-17
lines changed

‎src/backend/executor/execExprInterp.c

Lines changed: 42 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -501,47 +501,53 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
501501
EEO_CASE(EEOP_INNER_SYSVAR)
502502
{
503503
intattnum=op->d.var.attnum;
504+
Datumd;
504505

505506
/* these asserts must match defenses in slot_getattr */
506507
Assert(innerslot->tts_tuple!=NULL);
507508
Assert(innerslot->tts_tuple!=&(innerslot->tts_minhdr));
508-
/* heap_getsysattr has sufficient defenses against bad attnums */
509509

510-
*op->resvalue=heap_getsysattr(innerslot->tts_tuple,attnum,
511-
innerslot->tts_tupleDescriptor,
512-
op->resnull);
510+
/* heap_getsysattr has sufficient defenses against bad attnums */
511+
d=heap_getsysattr(innerslot->tts_tuple,attnum,
512+
innerslot->tts_tupleDescriptor,
513+
op->resnull);
514+
*op->resvalue=d;
513515

514516
EEO_NEXT();
515517
}
516518

517519
EEO_CASE(EEOP_OUTER_SYSVAR)
518520
{
519521
intattnum=op->d.var.attnum;
522+
Datumd;
520523

521524
/* these asserts must match defenses in slot_getattr */
522525
Assert(outerslot->tts_tuple!=NULL);
523526
Assert(outerslot->tts_tuple!=&(outerslot->tts_minhdr));
524527

525528
/* heap_getsysattr has sufficient defenses against bad attnums */
526-
*op->resvalue=heap_getsysattr(outerslot->tts_tuple,attnum,
527-
outerslot->tts_tupleDescriptor,
528-
op->resnull);
529+
d=heap_getsysattr(outerslot->tts_tuple,attnum,
530+
outerslot->tts_tupleDescriptor,
531+
op->resnull);
532+
*op->resvalue=d;
529533

530534
EEO_NEXT();
531535
}
532536

533537
EEO_CASE(EEOP_SCAN_SYSVAR)
534538
{
535539
intattnum=op->d.var.attnum;
540+
Datumd;
536541

537542
/* these asserts must match defenses in slot_getattr */
538543
Assert(scanslot->tts_tuple!=NULL);
539544
Assert(scanslot->tts_tuple!=&(scanslot->tts_minhdr));
540-
/* heap_getsysattr has sufficient defenses against bad attnums */
541545

542-
*op->resvalue=heap_getsysattr(scanslot->tts_tuple,attnum,
543-
scanslot->tts_tupleDescriptor,
544-
op->resnull);
546+
/* heap_getsysattr has sufficient defenses against bad attnums */
547+
d=heap_getsysattr(scanslot->tts_tuple,attnum,
548+
scanslot->tts_tupleDescriptor,
549+
op->resnull);
550+
*op->resvalue=d;
545551

546552
EEO_NEXT();
547553
}
@@ -641,13 +647,22 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
641647
* As both STRICT checks and function-usage are noticeable performance
642648
* wise, and function calls are a very hot-path (they also back
643649
* operators!), it's worth having so many separate opcodes.
650+
*
651+
* Note: the reason for using a temporary variable "d", here and in
652+
* other places, is that some compilers think "*op->resvalue = f();"
653+
* requires them to evaluate op->resvalue into a register before
654+
* calling f(), just in case f() is able to modify op->resvalue
655+
* somehow. The extra line of code can save a useless register spill
656+
* and reload across the function call.
644657
*/
645658
EEO_CASE(EEOP_FUNCEXPR)
646659
{
647660
FunctionCallInfofcinfo=op->d.func.fcinfo_data;
661+
Datumd;
648662

649663
fcinfo->isnull= false;
650-
*op->resvalue=op->d.func.fn_addr(fcinfo);
664+
d=op->d.func.fn_addr(fcinfo);
665+
*op->resvalue=d;
651666
*op->resnull=fcinfo->isnull;
652667

653668
EEO_NEXT();
@@ -658,6 +673,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
658673
FunctionCallInfofcinfo=op->d.func.fcinfo_data;
659674
bool*argnull=fcinfo->argnull;
660675
intargno;
676+
Datumd;
661677

662678
/* strict function, so check for NULL args */
663679
for (argno=0;argno<op->d.func.nargs;argno++)
@@ -669,7 +685,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
669685
}
670686
}
671687
fcinfo->isnull= false;
672-
*op->resvalue=op->d.func.fn_addr(fcinfo);
688+
d=op->d.func.fn_addr(fcinfo);
689+
*op->resvalue=d;
673690
*op->resnull=fcinfo->isnull;
674691

675692
strictfail:
@@ -680,11 +697,13 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
680697
{
681698
FunctionCallInfofcinfo=op->d.func.fcinfo_data;
682699
PgStat_FunctionCallUsagefcusage;
700+
Datumd;
683701

684702
pgstat_init_function_usage(fcinfo,&fcusage);
685703

686704
fcinfo->isnull= false;
687-
*op->resvalue=op->d.func.fn_addr(fcinfo);
705+
d=op->d.func.fn_addr(fcinfo);
706+
*op->resvalue=d;
688707
*op->resnull=fcinfo->isnull;
689708

690709
pgstat_end_function_usage(&fcusage, true);
@@ -698,6 +717,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
698717
PgStat_FunctionCallUsagefcusage;
699718
bool*argnull=fcinfo->argnull;
700719
intargno;
720+
Datumd;
701721

702722
/* strict function, so check for NULL args */
703723
for (argno=0;argno<op->d.func.nargs;argno++)
@@ -712,7 +732,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
712732
pgstat_init_function_usage(fcinfo,&fcusage);
713733

714734
fcinfo->isnull= false;
715-
*op->resvalue=op->d.func.fn_addr(fcinfo);
735+
d=op->d.func.fn_addr(fcinfo);
736+
*op->resvalue=d;
716737
*op->resnull=fcinfo->isnull;
717738

718739
pgstat_end_function_usage(&fcusage, true);
@@ -1113,14 +1134,16 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
11131134
if (!op->d.iocoerce.finfo_in->fn_strict||str!=NULL)
11141135
{
11151136
FunctionCallInfofcinfo_in;
1137+
Datumd;
11161138

11171139
fcinfo_in=op->d.iocoerce.fcinfo_data_in;
11181140
fcinfo_in->arg[0]=PointerGetDatum(str);
11191141
fcinfo_in->argnull[0]=*op->resnull;
11201142
/* second and third arguments are already set up */
11211143

11221144
fcinfo_in->isnull= false;
1123-
*op->resvalue=FunctionCallInvoke(fcinfo_in);
1145+
d=FunctionCallInvoke(fcinfo_in);
1146+
*op->resvalue=d;
11241147

11251148
/* Should get null result if and only if str is NULL */
11261149
if (str==NULL)
@@ -1268,6 +1291,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
12681291
EEO_CASE(EEOP_ROWCOMPARE_STEP)
12691292
{
12701293
FunctionCallInfofcinfo=op->d.rowcompare_step.fcinfo_data;
1294+
Datumd;
12711295

12721296
/* force NULL result if strict fn and NULL input */
12731297
if (op->d.rowcompare_step.finfo->fn_strict&&
@@ -1279,7 +1303,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
12791303

12801304
/* Apply comparison function */
12811305
fcinfo->isnull= false;
1282-
*op->resvalue=op->d.rowcompare_step.fn_addr(fcinfo);
1306+
d=op->d.rowcompare_step.fn_addr(fcinfo);
1307+
*op->resvalue=d;
12831308

12841309
/* force NULL result if NULL function result */
12851310
if (fcinfo->isnull)

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