Andres Freund <and...@anarazel.de> writes:
> On 2017-09-28 16:21:34 -0400, Tom Lane wrote:
>> We could save a pointless register spill
>> and reload if there were a temporary variable in there,
> Makes sense. Do you want to make it so, or shall I?
I just finished testing a patch, as attached. On my machine (again,
not latest gcc: 4.4.7 on RHEL6 x86_64), it reduces the code size of
execExprInterp.o by a fraction of a percent, and it seems to offer
a slight benefit in "pgbench -S" performance although I'd not put
much stock in that being reproducible.
> I'd personally be
> somewhat tempted to keep the branches in sync here...
I was tempted that way too, but it doesn't apply cleanly to v10,
because of Peter's recent cleanup of function pointer invocation
style. I don't think it's really worth worrying about.
regards, tom lane
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 09abd46..68a1f96 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -501,15 +501,17 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
EEO_CASE(EEOP_INNER_SYSVAR)
{
int attnum = op->d.var.attnum;
+ Datum d;
/* these asserts must match defenses in slot_getattr */
Assert(innerslot->tts_tuple != NULL);
Assert(innerslot->tts_tuple != &(innerslot->tts_minhdr));
- /* heap_getsysattr has sufficient defenses against bad attnums */
- *op->resvalue = heap_getsysattr(innerslot->tts_tuple, attnum,
- innerslot->tts_tupleDescriptor,
- op->resnull);
+ /* heap_getsysattr has sufficient defenses against bad attnums */
+ d = heap_getsysattr(innerslot->tts_tuple, attnum,
+ innerslot->tts_tupleDescriptor,
+ op->resnull);
+ *op->resvalue = d;
EEO_NEXT();
}
@@ -517,15 +519,17 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
EEO_CASE(EEOP_OUTER_SYSVAR)
{
int attnum = op->d.var.attnum;
+ Datum d;
/* these asserts must match defenses in slot_getattr */
Assert(outerslot->tts_tuple != NULL);
Assert(outerslot->tts_tuple != &(outerslot->tts_minhdr));
/* heap_getsysattr has sufficient defenses against bad attnums */
- *op->resvalue = heap_getsysattr(outerslot->tts_tuple, attnum,
- outerslot->tts_tupleDescriptor,
- op->resnull);
+ d = heap_getsysattr(outerslot->tts_tuple, attnum,
+ outerslot->tts_tupleDescriptor,
+ op->resnull);
+ *op->resvalue = d;
EEO_NEXT();
}
@@ -533,15 +537,17 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
EEO_CASE(EEOP_SCAN_SYSVAR)
{
int attnum = op->d.var.attnum;
+ Datum d;
/* these asserts must match defenses in slot_getattr */
Assert(scanslot->tts_tuple != NULL);
Assert(scanslot->tts_tuple != &(scanslot->tts_minhdr));
- /* heap_getsysattr has sufficient defenses against bad attnums */
- *op->resvalue = heap_getsysattr(scanslot->tts_tuple, attnum,
- scanslot->tts_tupleDescriptor,
- op->resnull);
+ /* heap_getsysattr has sufficient defenses against bad attnums */
+ d = heap_getsysattr(scanslot->tts_tuple, attnum,
+ scanslot->tts_tupleDescriptor,
+ op->resnull);
+ *op->resvalue = d;
EEO_NEXT();
}
@@ -641,13 +647,22 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
* As both STRICT checks and function-usage are noticeable performance
* wise, and function calls are a very hot-path (they also back
* operators!), it's worth having so many separate opcodes.
+ *
+ * Note: the reason for using a temporary variable "d", here and in
+ * other places, is that some compilers think "*op->resvalue = f();"
+ * requires them to evaluate op->resvalue into a register before
+ * calling f(), just in case f() is able to modify op->resvalue
+ * somehow. The extra line of code can save a useless register spill
+ * and reload, on architectures without many registers.
*/
EEO_CASE(EEOP_FUNCEXPR)
{
FunctionCallInfo fcinfo = op->d.func.fcinfo_data;
+ Datum d;
fcinfo->isnull = false;
- *op->resvalue = op->d.func.fn_addr(fcinfo);
+ d = op->d.func.fn_addr(fcinfo);
+ *op->resvalue = d;
*op->resnull = fcinfo->isnull;
EEO_NEXT();
@@ -658,6 +673,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
FunctionCallInfo fcinfo = op->d.func.fcinfo_data;
bool *argnull = fcinfo->argnull;
int argno;
+ Datum d;
/* strict function, so check for NULL args */
for (argno = 0; argno < op->d.func.nargs; argno++)
@@ -669,7 +685,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
}
}
fcinfo->isnull = false;
- *op->resvalue = op->d.func.fn_addr(fcinfo);
+ d = op->d.func.fn_addr(fcinfo);
+ *op->resvalue = d;
*op->resnull = fcinfo->isnull;
strictfail:
@@ -680,11 +697,13 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
{
FunctionCallInfo fcinfo = op->d.func.fcinfo_data;
PgStat_FunctionCallUsage fcusage;
+ Datum d;
pgstat_init_function_usage(fcinfo, &fcusage);
fcinfo->isnull = false;
- *op->resvalue = op->d.func.fn_addr(fcinfo);
+ d = op->d.func.fn_addr(fcinfo);
+ *op->resvalue = d;
*op->resnull = fcinfo->isnull;
pgstat_end_function_usage(&fcusage, true);
@@ -698,6 +717,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
PgStat_FunctionCallUsage fcusage;
bool *argnull = fcinfo->argnull;
int argno;
+ Datum d;
/* strict function, so check for NULL args */
for (argno = 0; argno < op->d.func.nargs; argno++)
@@ -712,7 +732,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
pgstat_init_function_usage(fcinfo, &fcusage);
fcinfo->isnull = false;
- *op->resvalue = op->d.func.fn_addr(fcinfo);
+ d = op->d.func.fn_addr(fcinfo);
+ *op->resvalue = d;
*op->resnull = fcinfo->isnull;
pgstat_end_function_usage(&fcusage, true);
@@ -1113,6 +1134,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
if (!op->d.iocoerce.finfo_in->fn_strict || str != NULL)
{
FunctionCallInfo fcinfo_in;
+ Datum d;
fcinfo_in = op->d.iocoerce.fcinfo_data_in;
fcinfo_in->arg[0] = PointerGetDatum(str);
@@ -1120,7 +1142,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
/* second and third arguments are already set up */
fcinfo_in->isnull = false;
- *op->resvalue = FunctionCallInvoke(fcinfo_in);
+ d = FunctionCallInvoke(fcinfo_in);
+ *op->resvalue = d;
/* Should get null result if and only if str is NULL */
if (str == NULL)
@@ -1268,6 +1291,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
EEO_CASE(EEOP_ROWCOMPARE_STEP)
{
FunctionCallInfo fcinfo = op->d.rowcompare_step.fcinfo_data;
+ Datum d;
/* force NULL result if strict fn and NULL input */
if (op->d.rowcompare_step.finfo->fn_strict &&
@@ -1279,7 +1303,8 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
/* Apply comparison function */
fcinfo->isnull = false;
- *op->resvalue = op->d.rowcompare_step.fn_addr(fcinfo);
+ d = op->d.rowcompare_step.fn_addr(fcinfo);
+ *op->resvalue = d;
/* force NULL result if NULL function result */
if (fcinfo->isnull)
--
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