Turn SECONDARY_MEMORY_NEEDED_MODE into a target hook

This includes a change to LRA.  Previously the code was:

    if (sclass == NO_REGS && dclass == NO_REGS)
      return false;
  #ifdef SECONDARY_MEMORY_NEEDED
    if (SECONDARY_MEMORY_NEEDED (sclass, dclass, GET_MODE (src))
  #ifdef SECONDARY_MEMORY_NEEDED_MODE
        && ((sclass != NO_REGS && dclass != NO_REGS)
            || GET_MODE (src) != SECONDARY_MEMORY_NEEDED_MODE (GET_MODE (src)))
  #endif
        )
      {
        *sec_mem_p = true;
        return false;
      }
  #endif

in which the positioning of the second ifdef meant that defining
SECONDARY_MEMORY_NEEDED_MODE to its default value was not a no-op:
without a definition, we would consider using secondary reloads for
mem<-reg and reg<-mem reloads even if the secondary memory has the
same mode as the original mem, while defining it would avoid this.
The latter behaviour seems correct.

The default is different for reload and LRA.  For LRA the default is
to use the original mode, while reload promotes smaller-than-word
integral modes to word mode:

  if (GET_MODE_BITSIZE (mode) < BITS_PER_WORD && INTEGRAL_MODE_P (mode))
    mode = mode_for_size (BITS_PER_WORD,
                          GET_MODE_CLASS (mode), 0).require ();

Some of the ports that have switched to LRA seemed to have
SECONDARY_MEMORY_NEEDED_MDOEs based on the old reload definition,
and still referred to the reload.c:get_secondary_mem function in
the comments.  The patch just keeps them as-is.

2017-09-13  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* target.def (secondary_memory_needed_mode): New hook:
	* targhooks.c (default_secondary_memory_needed_mode): Declare.
	* targhooks.h (default_secondary_memory_needed_mode): New function.
	* doc/tm.texi.in (SECONDARY_MEMORY_NEEDED_MODE): Replace with...
	(TARGET_SECONDARY_MEMORY_NEEDED_MODE): ...this.
	* doc/tm.texi: Regenerate.
	* lra-constraints.c (check_and_process_move): Use
	targetm.secondary_memory_needed_mode instead of
	TARGET_SECONDARY_MEMORY_NEEDED_MODE.
	(curr_insn_transform): Likewise.
	* reload.c (get_secondary_mem): Likewise.
	* config/alpha/alpha.h (SECONDARY_MEMORY_NEEDED_MODE): Delete.
	* config/alpha/alpha.c (alpha_secondary_memory_needed_mode): New
	function.
	(TARGET_SECONDARY_MEMORY_NEEDED_MODE): Redefine.
	* config/i386/i386.h (SECONDARY_MEMORY_NEEDED_MODE): Delete.
	* config/i386/i386.c (ix86_secondary_memory_needed_mode): New function.
	(TARGET_SECONDARY_MEMORY_NEEDED_MODE): Redefine.
	* config/powerpcspe/powerpcspe.h (SECONDARY_MEMORY_NEEDED_MODE):
	Delete.
	* config/powerpcspe/powerpcspe-protos.h
	(rs6000_secondary_memory_needed_mode): Delete.
	* config/powerpcspe/powerpcspe.c
	(TARGET_SECONDARY_MEMORY_NEEDED_MODE): Redefine.
	(rs6000_secondary_memory_needed_mode): Make static.
	* config/rs6000/rs6000.h (SECONDARY_MEMORY_NEEDED_MODE): Delete.
	* config/rs6000/rs6000-protos.h (rs6000_secondary_memory_needed_mode):
	Delete.
	* config/rs6000/rs6000.c (TARGET_SECONDARY_MEMORY_NEEDED_MODE):
	Redefine.
	(rs6000_secondary_memory_needed_mode): Make static.
	* config/s390/s390.h (SECONDARY_MEMORY_NEEDED_MODE): Delete.
	* config/s390/s390.c (s390_secondary_memory_needed_mode): New function.
	(TARGET_SECONDARY_MEMORY_NEEDED_MODE): Redefine.
	* config/sparc/sparc.h (SECONDARY_MEMORY_NEEDED_MODE): Delete.
	* config/sparc/sparc.c (TARGET_SECONDARY_MEMORY_NEEDED_MODE):
	Redefine.
	(sparc_secondary_memory_needed_mode): New function.
	* system.h (TARGET_SECONDARY_MEMORY_NEEDED_MODE): Poison.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r252455

2 files changed, 16 insertions, 40 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 98e6015..5e90208 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -2747,29 +2747,27 @@ Do not define this macro if you do not define
 @code{SECONDARY_MEMORY_NEEDED}.
 @end defmac
 
-@defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
-When the compiler needs a secondary memory location to copy between two
-registers of mode @var{mode}, it normally allocates sufficient memory to
-hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
-load operations in a mode that many bits wide and whose class is the
-same as that of @var{mode}.
-
-This is right thing to do on most machines because it ensures that all
-bits of the register are copied and prevents accesses to the registers
-in a narrower mode, which some machines prohibit for floating-point
-registers.
+@deftypefn {Target Hook} machine_mode TARGET_SECONDARY_MEMORY_NEEDED_MODE (machine_mode @var{mode})
+If @code{SECONDARY_MEMORY_NEEDED} tells the compiler to use memory
+when moving between two particular registers of mode @var{mode},
+this hook specifies the mode that the memory should have.
+
+The default depends on @code{TARGET_LRA_P}.  Without LRA, the default
+is to use a word-sized mode for integral modes that are smaller than a
+a word.  This is right thing to do on most machines because it ensures
+that all bits of the register are copied and prevents accesses to the
+registers in a narrower mode, which some machines prohibit for
+floating-point registers.
 
 However, this default behavior is not correct on some machines, such as
 the DEC Alpha, that store short integers in floating-point registers
 differently than in integer registers.  On those machines, the default
-widening will not work correctly and you must define this macro to
-suppress that widening in some cases.  See the file @file{alpha.h} for
+widening will not work correctly and you must define this hook to
+suppress that widening in some cases.  See the file @file{alpha.c} for
 details.
 
-Do not define this macro if you do not define
-@code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
-is @code{BITS_PER_WORD} bits wide is correct for your machine.
-@end defmac
+With LRA, the default is to use @var{mode} unmodified.
+@end deftypefn
 
 @deftypefn {Target Hook} bool TARGET_CLASS_LIKELY_SPILLED_P (reg_class_t @var{rclass})
 A target hook which returns @code{true} if pseudos that have been assigned
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index acf47e0..1919176 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -2324,29 +2324,7 @@ Do not define this macro if you do not define
 @code{SECONDARY_MEMORY_NEEDED}.
 @end defmac
 
-@defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
-When the compiler needs a secondary memory location to copy between two
-registers of mode @var{mode}, it normally allocates sufficient memory to
-hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
-load operations in a mode that many bits wide and whose class is the
-same as that of @var{mode}.
-
-This is right thing to do on most machines because it ensures that all
-bits of the register are copied and prevents accesses to the registers
-in a narrower mode, which some machines prohibit for floating-point
-registers.
-
-However, this default behavior is not correct on some machines, such as
-the DEC Alpha, that store short integers in floating-point registers
-differently than in integer registers.  On those machines, the default
-widening will not work correctly and you must define this macro to
-suppress that widening in some cases.  See the file @file{alpha.h} for
-details.
-
-Do not define this macro if you do not define
-@code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
-is @code{BITS_PER_WORD} bits wide is correct for your machine.
-@end defmac
+@hook TARGET_SECONDARY_MEMORY_NEEDED_MODE
 
 @hook TARGET_CLASS_LIKELY_SPILLED_P