Hi,
Now that we are OK with static inline functions, we can save some cycles
from floating-point functions, by turning Float4GetDatum,
Float8GetDatum, and DatumGetFloat8 into static inlines. They are only a
few instructions, but couldn't be implemented as macros before, because
they need a local union-variable for the conversion.
That can add up to significant speedups with float-heavy queries. For
example:
create table floats as select g::float8 as a, g::float8 as b, g::float8
as c from generate_series(1, 1000000) g;
select sum(a+b+c+1) from floats;
The sum query is about 4% faster on my laptop with this patch.
- Heikki
From 8ed0f619093b16d113a0f23ee903268799eb2212 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Wed, 31 Aug 2016 13:15:06 +0300
Subject: [PATCH] Use static inline functions for float <-> Datum conversions.
Now that we are OK with using static inline functions, we can use them
to avoid function call overhead for pass-by-val versions of Float4GetDatum,
DatumGetFloat8, and Float8GetDatum. Those functions are only a few CPU
instructions long, but they could not be written into macros previously,
because we needed a local union variable for the conversion.
I kept the pass-by-ref versions as regular functions. Those are very simple
too, but they call palloc() anyway, so shaving a few instructions from the
function call doesn't seem so important there.
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index 7e6a60d..7aae350 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -2126,10 +2126,7 @@ fmgr(Oid procedureId,...)
*
* int8, float4, and float8 can be passed by value if Datum is wide enough.
* (For backwards-compatibility reasons, we allow pass-by-ref to be chosen
- * at compile time even if pass-by-val is possible.) For the float types,
- * we need a support routine even if we are passing by value, because many
- * machines pass int and float function parameters/results differently;
- * so we need to play weird games with unions.
+ * at compile time even if pass-by-val is possible.)
*
* Note: there is only one switch controlling the pass-by-value option for
* both int8 and float8; this is to avoid making things unduly complicated
@@ -2149,77 +2146,29 @@ Int64GetDatum(int64 X)
}
#endif /* USE_FLOAT8_BYVAL */
+#ifndef USE_FLOAT4_BYVAL
+
Datum
Float4GetDatum(float4 X)
{
-#ifdef USE_FLOAT4_BYVAL
- union
- {
- float4 value;
- int32 retval;
- } myunion;
-
- myunion.value = X;
- return SET_4_BYTES(myunion.retval);
-#else
float4 *retval = (float4 *) palloc(sizeof(float4));
*retval = X;
return PointerGetDatum(retval);
-#endif
}
+#endif
-#ifdef USE_FLOAT4_BYVAL
-
-float4
-DatumGetFloat4(Datum X)
-{
- union
- {
- int32 value;
- float4 retval;
- } myunion;
-
- myunion.value = GET_4_BYTES(X);
- return myunion.retval;
-}
-#endif /* USE_FLOAT4_BYVAL */
+#ifndef USE_FLOAT8_BYVAL
Datum
Float8GetDatum(float8 X)
{
-#ifdef USE_FLOAT8_BYVAL
- union
- {
- float8 value;
- int64 retval;
- } myunion;
-
- myunion.value = X;
- return SET_8_BYTES(myunion.retval);
-#else
float8 *retval = (float8 *) palloc(sizeof(float8));
*retval = X;
return PointerGetDatum(retval);
-#endif
}
-
-#ifdef USE_FLOAT8_BYVAL
-
-float8
-DatumGetFloat8(Datum X)
-{
- union
- {
- int64 value;
- float8 retval;
- } myunion;
-
- myunion.value = GET_8_BYTES(X);
- return myunion.retval;
-}
-#endif /* USE_FLOAT8_BYVAL */
+#endif
/*-------------------------------------------------------------------------
diff --git a/src/include/postgres.h b/src/include/postgres.h
index fb1933f..d999013 100644
--- a/src/include/postgres.h
+++ b/src/include/postgres.h
@@ -657,6 +657,14 @@ extern Datum Int64GetDatum(int64 X);
#endif
/*
+ * Float <-> Datum conversions
+ *
+ * These have to be implemented as inline functions rather than macros, when
+ * passing by value, because many machines pass int and float function
+ * parameters/results differently; so we need to play weird games with unions.
+ */
+
+/*
* DatumGetFloat4
* Returns 4-byte floating point value of a datum.
*
@@ -664,7 +672,18 @@ extern Datum Int64GetDatum(int64 X);
*/
#ifdef USE_FLOAT4_BYVAL
-extern float4 DatumGetFloat4(Datum X);
+static inline float4
+DatumGetFloat4(Datum X)
+{
+ union
+ {
+ int32 value;
+ float4 retval;
+ } myunion;
+
+ myunion.value = GET_4_BYTES(X);
+ return myunion.retval;
+}
#else
#define DatumGetFloat4(X) (* ((float4 *) DatumGetPointer(X)))
#endif
@@ -676,8 +695,22 @@ extern float4 DatumGetFloat4(Datum X);
* Note: if float4 is pass by reference, this function returns a reference
* to palloc'd space.
*/
+#ifdef USE_FLOAT4_BYVAL
+static inline Datum
+Float4GetDatum(float4 X)
+{
+ union
+ {
+ float4 value;
+ int32 retval;
+ } myunion;
+ myunion.value = X;
+ return SET_4_BYTES(myunion.retval);
+}
+#else
extern Datum Float4GetDatum(float4 X);
+#endif
/*
* DatumGetFloat8
@@ -687,7 +720,18 @@ extern Datum Float4GetDatum(float4 X);
*/
#ifdef USE_FLOAT8_BYVAL
-extern float8 DatumGetFloat8(Datum X);
+static inline float8
+DatumGetFloat8(Datum X)
+{
+ union
+ {
+ int64 value;
+ float8 retval;
+ } myunion;
+
+ myunion.value = GET_8_BYTES(X);
+ return myunion.retval;
+}
#else
#define DatumGetFloat8(X) (* ((float8 *) DatumGetPointer(X)))
#endif
@@ -700,7 +744,22 @@ extern float8 DatumGetFloat8(Datum X);
* to palloc'd space.
*/
+#ifdef USE_FLOAT8_BYVAL
+static inline Datum
+Float8GetDatum(float8 X)
+{
+ union
+ {
+ float8 value;
+ int64 retval;
+ } myunion;
+
+ myunion.value = X;
+ return SET_8_BYTES(myunion.retval);
+}
+#else
extern Datum Float8GetDatum(float8 X);
+#endif
/*
--
2.9.3
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
