Disabling string evaluation in a logging system
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From: Stephen Leake on 19 May 2010 05:04 dhenry <tfc.duke(a)gmail.com> writes: > As Dmitry said, the log level may dynamically change. Therefore, > inlining in order to let the compiler do the optimization doesn't > work. I don't follow this. Inlining is the same as writing the if-test. Given this: procedure Inlined_Log (S : in string; Level : in Level_Type) is begin if Level > Global_Level then put (S); end if; end Inlined_Log; then the compiler (with the right switches) should convert this: begin Inlined_Log (<expression>, A_Log_Level); end; to this: begin if A_Log_Level > Global_Level then put (A_Log_Level); end if; end; What is the problem? -- -- Stephe
From: Dmitry A. Kazakov on 19 May 2010 08:38 On Wed, 19 May 2010 05:04:32 -0400, Stephen Leake wrote: > dhenry <tfc.duke(a)gmail.com> writes: > >> As Dmitry said, the log level may dynamically change. Therefore, >> inlining in order to let the compiler do the optimization doesn't >> work. > > I don't follow this. Inlining is the same as writing the if-test. That depends on the compiler. procedure Log (Barrier : Boolean; Message : String) is begin if Barrier then Put (Message); end if; end Log; can be inlined as: 1. moving evaluation of temporaries down: declare Barrier : constant Boolean := <condition-expression>; begin if Barrier then declare Message : constant String := <message-expression>; begin Put (Message); end; end if; end; or as 2. moving evaluation of temporaries up: declare Barrier : constant Boolean := <condition-expression>; Message : constant String := <message-expression>; begin if Barrier then Put (Message); end if; end; The language mandates nothing regarding this. The compiler can even ignore the pragma Inline. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de
From: (see below) on 19 May 2010 14:02 On 19/05/2010 13:38, in article 1p3xrphlq60da.1cq62wm0ajal2$.dlg(a)40tude.net, "Dmitry A. Kazakov" <mailbox(a)dmitry-kazakov.de> wrote: > On Wed, 19 May 2010 05:04:32 -0400, Stephen Leake wrote: > >> dhenry <tfc.duke(a)gmail.com> writes: >> >>> As Dmitry said, the log level may dynamically change. Therefore, >>> inlining in order to let the compiler do the optimization doesn't >>> work. >> >> I don't follow this. Inlining is the same as writing the if-test. > > That depends on the compiler. > > procedure Log (Barrier : Boolean; Message : String) is > begin > if Barrier then > Put (Message); > end if; > end Log; > > can be inlined as: > > 1. moving evaluation of temporaries down: > > declare > Barrier : constant Boolean := <condition-expression>; > begin > if Barrier then > declare > Message : constant String := <message-expression>; > begin > Put (Message); > end; > end if; > end; > > or as > > 2. moving evaluation of temporaries up: > > declare > Barrier : constant Boolean := <condition-expression>; > Message : constant String := <message-expression>; > begin > if Barrier then > Put (Message); > end if; > end; > > The language mandates nothing regarding this. The compiler can even ignore > the pragma Inline. I thought the second would be required, to allow side effects to take place as they would normally. -- Bill Findlay <surname><forename> chez blueyonder.co.uk
From: Adam Beneschan on 19 May 2010 15:08
On May 19, 11:02 am, "(see below)" <yaldni...(a)blueyonder.co.uk> wrote: > On 19/05/2010 13:38, in article 1p3xrphlq60da.1cq62wm0ajal2$....@40tude.net, > "Dmitry A. Kazakov" <mail...(a)dmitry-kazakov.de> wrote: > > > > > > > On Wed, 19 May 2010 05:04:32 -0400, Stephen Leake wrote: > > >> dhenry <tfc.d...(a)gmail.com> writes: > > >>> As Dmitry said, the log level may dynamically change. Therefore, > >>> inlining in order to let the compiler do the optimization doesn't > >>> work. > > >> I don't follow this. Inlining is the same as writing the if-test. > > > That depends on the compiler. > > > procedure Log (Barrier : Boolean; Message : String) is > > begin > > if Barrier then > > Put (Message); > > end if; > > end Log; > > > can be inlined as: > > > 1. moving evaluation of temporaries down: > > > declare > > Barrier : constant Boolean := <condition-expression>; > > begin > > if Barrier then > > declare > > Message : constant String := <message-expression>; > > begin > > Put (Message); > > end; > > end if; > > end; > > > or as > > > 2. moving evaluation of temporaries up: > > > declare > > Barrier : constant Boolean := <condition-expression>; > > Message : constant String := <message-expression>; > > begin > > if Barrier then > > Put (Message); > > end if; > > end; > > > The language mandates nothing regarding this. The compiler can even ignore > > the pragma Inline. > > I thought the second would be required, to allow side effects to take place > as they would normally. I think that if the compiler can determine that the message-expression will not have any side effects, or that the only possible side effects are language-defined exceptions (or something like that), it doesn't have to evaluate it if it can tell the result won't be used. In the OP's original example, assuming that To_String is Ada.Strings.Unbounded.To_String (we can't tell), it should be OK. -- Adam |