diff options
Diffstat (limited to 'gcc/ada/exp_ch5.adb')
| -rw-r--r-- | gcc/ada/exp_ch5.adb | 85 |
1 files changed, 50 insertions, 35 deletions
diff --git a/gcc/ada/exp_ch5.adb b/gcc/ada/exp_ch5.adb index 8105de381d2..a257b274ce0 100644 --- a/gcc/ada/exp_ch5.adb +++ b/gcc/ada/exp_ch5.adb @@ -95,24 +95,6 @@ package body Exp_Ch5 is -- either because the target is not byte aligned, or there is a change -- of representation. - function Maybe_Bit_Aligned_Large_Component (N : Node_Id) return Boolean; - -- This function is used in processing the assignment of a record or - -- indexed component. The back end can handle such assignments fine - -- if the objects involved are small (64-bits) or are both aligned on - -- a byte boundary (starts on a byte, and ends on a byte). However, - -- problems arise for large components that are not byte aligned, - -- since the assignment may clobber other components that share bit - -- positions in the starting or ending bytes, and in the case of - -- components not starting on a byte boundary, the back end cannot - -- even manage to extract the value. This function is used to detect - -- such situations, so that the assignment can be handled component-wise. - -- A value of False means that either the object is known to be greater - -- than 64 bits, or that it is known to be byte aligned (and occupy an - -- integral number of bytes. True is returned if the object is known to - -- be greater than 64 bits, and is known to be unaligned. As implied - -- by the name, the result is conservative, in that if the compiler - -- cannot determine these conditions at compile time, True is returned. - function Make_Tag_Ctrl_Assignment (N : Node_Id) return List_Id; -- Generate the necessary code for controlled and Tagged assignment, -- that is to say, finalization of the target before, adjustement of @@ -120,13 +102,41 @@ package body Exp_Ch5 is -- pointers which are not 'part of the value' and must not be changed -- upon assignment. N is the original Assignment node. + function Possible_Bit_Aligned_Component (N : Node_Id) return Boolean; + -- This function is used in processing the assignment of a record or + -- indexed component. The back end can handle such assignments fine + -- if the objects involved are small (64-bits or less) records or + -- scalar items (including bit-packed arrays represented with modular + -- types) or are both aligned on a byte boundary (starting on a byte + -- boundary, and occupying an integral number of bytes). + -- + -- However, problems arise for records larger than 64 bits, or for + -- arrays (other than bit-packed arrays represented with a modular + -- type) if the component starts on a non-byte boundary, or does + -- not occupy an integral number of bytes (i.e. there are some bits + -- possibly shared with fields at the start or beginning of the + -- component). The back end cannot handle loading and storing such + -- components in a single operation. + -- + -- This function is used to detect the troublesome situation. it is + -- conservative in the sense that it produces True unless it knows + -- for sure that the component is safe (as outlined in the first + -- paragraph above). The code generation for record and array + -- assignment checks for trouble using this function, and if so + -- the assignment is generated component-wise, which the back end + -- is required to handle correctly. + -- + -- Note that in GNAT 3, the back end will reject such components + -- anyway, so the hard work in checking for this case is wasted + -- in GNAT 3, but it's harmless, so it is easier to do it in + -- all cases, rather than conditionalize it in GNAT 5 or beyond. + ------------------------------ -- Change_Of_Representation -- ------------------------------ function Change_Of_Representation (N : Node_Id) return Boolean is Rhs : constant Node_Id := Expression (N); - begin return Nkind (Rhs) = N_Type_Conversion @@ -372,9 +382,9 @@ package body Exp_Ch5 is -- We require a loop if the left side is possibly bit unaligned - elsif Maybe_Bit_Aligned_Large_Component (Lhs) + elsif Possible_Bit_Aligned_Component (Lhs) or else - Maybe_Bit_Aligned_Large_Component (Rhs) + Possible_Bit_Aligned_Component (Rhs) then Loop_Required := True; @@ -1026,9 +1036,9 @@ package body Exp_Ch5 is -- clobbering of other components sharing bits in the first or -- last byte of the component to be assigned. - elsif Maybe_Bit_Aligned_Large_Component (Lhs) + elsif Possible_Bit_Aligned_Component (Lhs) or - Maybe_Bit_Aligned_Large_Component (Rhs) + Possible_Bit_Aligned_Component (Rhs) then null; @@ -3221,11 +3231,11 @@ package body Exp_Ch5 is return Empty_List; end Make_Tag_Ctrl_Assignment; - --------------------------------------- - -- Maybe_Bit_Aligned_Large_Component -- - --------------------------------------- + ------------------------------------ + -- Possible_Bit_Aligned_Component -- + ------------------------------------ - function Maybe_Bit_Aligned_Large_Component (N : Node_Id) return Boolean is + function Possible_Bit_Aligned_Component (N : Node_Id) return Boolean is begin case Nkind (N) is @@ -3250,7 +3260,7 @@ package body Exp_Ch5 is -- indexing from a possibly unaligned component. else - return Maybe_Bit_Aligned_Large_Component (P); + return Possible_Bit_Aligned_Component (P); end if; end; @@ -3268,17 +3278,22 @@ package body Exp_Ch5 is -- only the recursive test on the prefix. if No (Component_Clause (Comp)) then - return Maybe_Bit_Aligned_Large_Component (P); + return Possible_Bit_Aligned_Component (P); -- Otherwise we have a component clause, which means that -- the Esize and Normalized_First_Bit fields are set and -- contain static values known at compile time. else - -- If we know the size is 64 bits or less we are fine - -- since the back end always handles small fields right. - - if Esize (Comp) <= 64 then + -- If we know that we have a small (64 bits or less) record + -- or bit-packed array, then everything is fine, since the + -- back end can handle these cases correctly. + + if Esize (Comp) <= 64 + and then (Is_Record_Type (Etype (Comp)) + or else + Is_Bit_Packed_Array (Etype (Comp))) + then return False; -- Otherwise if the component is not byte aligned, we @@ -3293,7 +3308,7 @@ package body Exp_Ch5 is -- but we still need to test our prefix recursively. else - return Maybe_Bit_Aligned_Large_Component (P); + return Possible_Bit_Aligned_Component (P); end if; end if; end; @@ -3306,6 +3321,6 @@ package body Exp_Ch5 is return False; end case; - end Maybe_Bit_Aligned_Large_Component; + end Possible_Bit_Aligned_Component; end Exp_Ch5; |