diff --git a/gcc/ChangeLog b/gcc/ChangeLog index d4bfab0b494..4d1586dd01a 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +Tue Apr 21 16:36:01 1998 John Carr + + * alias.c (mode_alias_check): New function. + (true_dependence, anti_dependence, output_dependence): Call + mode_alias_check. + Tue Apr 21 12:05:32 1998 Jeffrey A Law (law@cygnus.com) * c-common.c (type_for_mode): Handle TI types. diff --git a/gcc/alias.c b/gcc/alias.c index ffd20ec98f9..bc0b49c2322 100644 --- a/gcc/alias.c +++ b/gcc/alias.c @@ -35,6 +35,7 @@ static int memrefs_conflict_p PROTO((int, rtx, int, rtx, static void record_set PROTO((rtx, rtx)); static rtx find_base_term PROTO((rtx)); static int base_alias_check PROTO((rtx, rtx)); +static int mode_alias_check PROTO((rtx, rtx, int (*)(rtx))); /* Set up all info needed to perform alias analysis on memory references. */ @@ -633,7 +634,11 @@ base_alias_check (x, y) align memory references, as is done on the Alpha. Nice to notice that varying addresses cannot conflict with fp if no - local variables had their addresses taken, but that's too hard now. */ + local variables had their addresses taken, but that's too hard now. + + TODO: (symbol_ref foo) can not alias (plus REG N) if N is a positive + integer because REG would have to point outside of the object, which + is not allowed in C or C++. */ static int @@ -815,6 +820,64 @@ memrefs_conflict_p (xsize, x, ysize, y, c) generate aligned addresses from unaligned addresses, for instance, the alpha storeqi_unaligned pattern. */ + +/* This subroutine implements the type and struct/varying part of the + alias check. + + Return 0 if the memory references can never alias. + Return 1 if the values of the addresses should be checked. */ + +static int +mode_alias_check (x, y, varies) + register rtx x, y; + int (*varies) PROTO ((rtx)); +{ + enum machine_mode x_mode = GET_MODE (x), y_mode = GET_MODE (y); + rtx x_addr = XEXP (x, 0), y_addr = XEXP (y, 0); + int x_varies, y_varies, x_struct, y_struct; + + /* If either address is an AND then neither the mode check nor the + struct/varying check is valid. */ + if (GET_CODE (x_addr) == AND || GET_CODE (y_addr) == AND) + return 1; + + x_struct = MEM_IN_STRUCT_P (x); + y_struct = MEM_IN_STRUCT_P (y); + + /* QImode and BLKmode references can alias anything. */ + if (x_mode == QImode || x_mode == BLKmode + || y_mode == QImode || y_mode == BLKmode) + return 1; + + /* Otherwise, different modes can only alias if they are structure + references. gcc bitfield operations can access an entire word, + but that word may also contain integers accessed directly. + + ??? It appears that bitfield accesses can not be larger than + word_mode? + ??? Can complex modes alias their components? */ + if (x_mode != y_mode && ! (x_struct && y_struct)) + return 0; + + /* Modes are the same or may alias. */ + + /* No alias if one reference is a struct at a varying address and the + other is a scalar at a fixed address. + + If either reference is a varying scalar or a fixed struct nothing + is known about aliasing. */ + x_varies = varies (x_addr); + if (x_struct != x_varies) + return 1; + y_varies = varies (y_addr); + if (y_struct != y_varies) + return 1; + + /* Both are varying structs or fixed scalars. Check that they are not + the same type. */ + return (x_struct == y_struct); +} + /* Read dependence: X is read after read in MEM takes place. There can only be a dependence here if both reads are volatile. */ @@ -853,40 +916,17 @@ true_dependence (mem, mem_mode, x, varies) if (! base_alias_check (XEXP (x, 0), XEXP (mem, 0))) return 0; + if (! mode_alias_check (x, mem, varies)) + return 0; + x_addr = canon_rtx (XEXP (x, 0)); mem_addr = canon_rtx (XEXP (mem, 0)); if (mem_mode == VOIDmode) mem_mode = GET_MODE (mem); - if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr, - SIZE_FOR_MODE (x), x_addr, 0)) - return 0; - - /* If both references are struct references, or both are not, nothing - is known about aliasing. - - If either reference is QImode or BLKmode, ANSI C permits aliasing. - - If both addresses are constant, or both are not, nothing is known - about aliasing. */ - if (MEM_IN_STRUCT_P (x) == MEM_IN_STRUCT_P (mem) - || mem_mode == QImode || mem_mode == BLKmode - || GET_MODE (x) == QImode || GET_MODE (x) == BLKmode - || GET_CODE (x_addr) == AND || GET_CODE (mem_addr) == AND - || varies (x_addr) == varies (mem_addr)) - return 1; - - /* One memory reference is to a constant address, one is not. - One is to a structure, the other is not. - - If either memory reference is a variable structure the other is a - fixed scalar and there is no aliasing. */ - if ((MEM_IN_STRUCT_P (mem) && varies (mem_addr)) - || (MEM_IN_STRUCT_P (x) && varies (x_addr))) - return 0; - - return 1; + return memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr, + SIZE_FOR_MODE (x), x_addr, 0); } /* Anti dependence: X is written after read in MEM takes place. */ @@ -916,16 +956,11 @@ anti_dependence (mem, x) x_addr = XEXP (x, 0); mem_addr = XEXP (mem, 0); - return (memrefs_conflict_p (SIZE_FOR_MODE (mem), mem_addr, - SIZE_FOR_MODE (x), x_addr, 0) - && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem) - && GET_MODE (mem) != QImode - && GET_CODE (mem_addr) != AND - && ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x)) - && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x) - && GET_MODE (x) != QImode - && GET_CODE (x_addr) != AND - && ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem))); + if (! mode_alias_check (x, mem, rtx_varies_p)) + return 0; + + return memrefs_conflict_p (SIZE_FOR_MODE (mem), mem_addr, + SIZE_FOR_MODE (x), x_addr, 0); } /* Output dependence: X is written after store in MEM takes place. */ @@ -944,16 +979,11 @@ output_dependence (mem, x) x = canon_rtx (x); mem = canon_rtx (mem); - return (memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0), - SIZE_FOR_MODE (x), XEXP (x, 0), 0) - && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem) - && GET_MODE (mem) != QImode - && GET_CODE (XEXP (mem, 0)) != AND - && ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x)) - && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x) - && GET_MODE (x) != QImode - && GET_CODE (XEXP (x, 0)) != AND - && ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem))); + if (! mode_alias_check (x, mem, rtx_varies_p)) + return 0; + + return memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0), + SIZE_FOR_MODE (x), XEXP (x, 0), 0); }