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author | Eric Botcazou <ebotcazou@adacore.com> | 2022-06-16 13:22:18 +0200 |
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committer | Pierre-Marie de Rodat <derodat@adacore.com> | 2022-07-06 13:29:49 +0000 |
commit | cd7d1f448a4a826a4210121ed6bec989913ba4e7 (patch) | |
tree | f7d156baba193fc3eb1bbae1958e110714284605 /gcc | |
parent | e5802d60130bd804663559471f9c5f3561dfab4d (diff) | |
download | gcc-cd7d1f448a4a826a4210121ed6bec989913ba4e7.zip gcc-cd7d1f448a4a826a4210121ed6bec989913ba4e7.tar.gz gcc-cd7d1f448a4a826a4210121ed6bec989913ba4e7.tar.bz2 |
[Ada] Document the various function return mechanisms
gcc/ada/
* exp_ch6.adb (Function return mechanisms): New paragraph.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/ada/exp_ch6.adb | 43 |
1 files changed, 42 insertions, 1 deletions
diff --git a/gcc/ada/exp_ch6.adb b/gcc/ada/exp_ch6.adb index b5764ad..bf51e64 100644 --- a/gcc/ada/exp_ch6.adb +++ b/gcc/ada/exp_ch6.adb @@ -83,7 +83,48 @@ with Validsw; use Validsw; package body Exp_Ch6 is - -- Suffix for BIP formals + -------------------------------- + -- Function return mechanisms -- + -------------------------------- + + -- This is a summary of the various function return mechanisms implemented + -- in GNAT for Ada 2005 and later versions of the language. In the below + -- table, the first column must be read as an if expression: if the result + -- type of the function is limited, then the return mechanism is and ...; + -- elsif the result type is indefinite or large definite, then ...; elsif + -- ...; else ... The different mechanisms are implemented either in the + -- front end, or in the back end, or partly in both ends, depending on the + -- result type. + + -- Result type | Return mechanism | Front end | Back end + -- -------------------------------------------------------------------- + + -- Limited Build In Place All + + -- Indefinite/ Secondary Stack Needs Fin. Others + -- Large definite + + -- Needs Fin. Secondary Stack All + -- (BERS False) + + -- Needs Fin. Invisible Parameter All All + -- (BERS True) (return) (call) + + -- By Reference Invisible Parameter All + + -- Others Primary stack/ All + -- Registers + + -- Needs Fin.: type needs finalization [RM 7.6(9.1/2-9.6/2)] + -- BERS: Opt.Back_End_Return_Slot setting + + -- The table is valid for all calls except for those dispatching on result; + -- the latter calls are considered as returning a class-wide type and thus + -- always return on the secondary stack, with the help of a small wrapper + -- function (thunk) if the original result type is not itself returned on + -- the secondary stack as per the above table. + + -- Suffixes for Build-In-Place extra formals BIP_Alloc_Suffix : constant String := "BIPalloc"; BIP_Storage_Pool_Suffix : constant String := "BIPstoragepool"; |