This is a useful optimization to avoid contention around the shared
empty string.
Tested on x86_64-pc-linux-gnu, committed on trunk
2020-06-09 Arnaud Charlet <char...@adacore.com>
gcc/ada/
* libgnat/a-strunb__shared.ads, libgnat/a-strunb__shared.adb
(Reference, Unreference): No-op for Empty_Shared_String.
Remove unneeded calls to Reference.--- gcc/ada/libgnat/a-strunb__shared.adb
+++ gcc/ada/libgnat/a-strunb__shared.adb
@@ -73,7 +73,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Left string is empty, return Right string
@@ -112,7 +111,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Right is an empty string, return Left string
@@ -145,7 +143,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared one
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Left is empty string, return Right string
@@ -214,7 +211,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if Left = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -244,7 +240,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -277,7 +272,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Coefficient is one, just return string itself
@@ -506,7 +500,6 @@ package body Ada.Strings.Unbounded is
-- Empty string requested, return shared empty string
if Max_Length = 0 then
- Reference (Empty_Shared_String'Access);
return Empty_Shared_String'Access;
-- Otherwise, allocate requested space (and probably some more room)
@@ -701,7 +694,6 @@ package body Ada.Strings.Unbounded is
-- Result is an empty string, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -743,7 +735,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty, reuse shared empty string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -801,7 +792,6 @@ package body Ada.Strings.Unbounded is
-- effects if a program references an already-finalized object.
Object.Reference := Null_Unbounded_String.Reference;
- Reference (Object.Reference);
Unreference (SR);
end if;
end Finalize;
@@ -862,7 +852,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty, reuse shared empty string
if Count = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Length of the string is the same as requested, reuse source shared
@@ -912,7 +901,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty, reuse empty shared string
if Count = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1090,7 +1078,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Inserted string is empty, reuse source shared string
@@ -1132,7 +1119,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1197,7 +1183,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Result is same as source string, reuse source shared string
@@ -1241,7 +1226,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1276,6 +1260,10 @@ package body Ada.Strings.Unbounded is
procedure Reference (Item : not null Shared_String_Access) is
begin
+ if Item = Empty_Shared_String'Access then
+ return;
+ end if;
+
System.Atomic_Counters.Increment (Item.Counter);
end Reference;
@@ -1348,7 +1336,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise allocate new shared string and fill it
@@ -1397,7 +1384,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if DL = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1442,7 +1428,6 @@ package body Ada.Strings.Unbounded is
-- In case of empty string, reuse empty shared string
if Source'Length = 0 then
- Reference (Empty_Shared_String'Access);
Target.Reference := Empty_Shared_String'Access;
else
@@ -1504,7 +1489,6 @@ package body Ada.Strings.Unbounded is
-- For empty result reuse empty shared string
if Count = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Result is whole source string, reuse source shared string
@@ -1576,7 +1560,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty string, reuse empty shared string
if Count = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1619,7 +1602,6 @@ package body Ada.Strings.Unbounded is
begin
if Source'Length = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
else
@@ -1636,7 +1618,6 @@ package body Ada.Strings.Unbounded is
begin
if Length = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
else
@@ -1662,7 +1643,6 @@ package body Ada.Strings.Unbounded is
-- Nothing to translate, reuse empty shared string
if SR.Last = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -1726,7 +1706,6 @@ package body Ada.Strings.Unbounded is
-- Nothing to translate, reuse empty shared string
if SR.Last = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -1813,7 +1792,6 @@ package body Ada.Strings.Unbounded is
-- All blanks, reuse empty shared string
if Low = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
else
@@ -1867,7 +1845,6 @@ package body Ada.Strings.Unbounded is
-- All blanks, reuse empty shared string
if Low = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1929,7 +1906,6 @@ package body Ada.Strings.Unbounded is
-- string.
if Low = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
else
@@ -1940,7 +1916,6 @@ package body Ada.Strings.Unbounded is
-- is empty, reuse empty shared string.
if High = 0 or else DL = 0 then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -1973,7 +1948,6 @@ package body Ada.Strings.Unbounded is
-- string.
if Low = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -1985,7 +1959,6 @@ package body Ada.Strings.Unbounded is
-- is empty, reuse empty shared string.
if High = 0 or else DL = 0 then
- Reference (Empty_Shared_String'Access);
Source.Reference := Empty_Shared_String'Access;
Unreference (SR);
@@ -2029,7 +2002,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty slice, reuse empty shared string
elsif Low > High then
- Reference (Empty_Shared_String'Access);
DR := Empty_Shared_String'Access;
-- Otherwise, allocate new shared string and fill it
@@ -2064,7 +2036,6 @@ package body Ada.Strings.Unbounded is
-- Result is empty slice, reuse empty shared string
elsif Low > High then
- Reference (Empty_Shared_String'Access);
Target.Reference := Empty_Shared_String'Access;
Unreference (TR);
@@ -2101,14 +2072,12 @@ package body Ada.Strings.Unbounded is
Aux : Shared_String_Access := Item;
begin
- if System.Atomic_Counters.Decrement (Aux.Counter) then
-
- -- Reference counter of Empty_Shared_String should never reach
- -- zero. We check here in case it wraps around.
+ if Aux = Empty_Shared_String'Access then
+ return;
+ end if;
- if Aux /= Empty_Shared_String'Access then
- Free (Aux);
- end if;
+ if System.Atomic_Counters.Decrement (Aux.Counter) then
+ Free (Aux);
end if;
end Unreference;
--- gcc/ada/libgnat/a-strunb__shared.ads
+++ gcc/ada/libgnat/a-strunb__shared.ads
@@ -708,10 +708,12 @@ private
type Shared_String_Access is access all Shared_String;
procedure Reference (Item : not null Shared_String_Access);
- -- Increment reference counter
+ -- Increment reference counter.
+ -- Do nothing if Item points to Empty_Shared_String.
procedure Unreference (Item : not null Shared_String_Access);
- -- Decrement reference counter, deallocate Item when counter goes to zero
+ -- Decrement reference counter, deallocate Item when counter goes to zero.
+ -- Do nothing if Item points to Empty_Shared_String.
function Can_Be_Reused
(Item : not null Shared_String_Access;
