Re: Remove mode argument from gen_rtx_SET

[Jeff Law <law@redhat.com>]

On 05/07/2015 05:37 AM, Richard Sandiford wrote:
> One problem with the automatically-generated gen_rtx_FOO () macros
> is that they always have a mode parameter, even for codes like SET
> where the mode should always be VOIDmode.  This inevitably leads to
> cases where a caller accidentally passes something other than VOIDmode.
> E.g. when expanding an SImode move, the temptation is to make everything
> SImode, even the SETs.  This in turn can cause two instructions to appear
> different simply because their SETs have different modes, even though the
> SET_DEST and SET_SRC are identical.
>
> E.g. for gcc/testsuite/g++.dg/torture/pr34651.C on lm32-elf we have
> the following before jump2:
>
>    (jump_insn 42 191 43 5 (set (pc)
> 	  (if_then_else (eq:SI (reg:SI 13 r13 [orig:43 inHotKey$4+-3 ] [43])
> 		  (const_int 0 [0]))
> 	      (label_ref 53)
> 	      (pc))) gcc/testsuite/g++.dg/torture/pr34651.C:22 22 {*beq}
>         (expr_list:REG_DEAD (reg:SI 13 r13 [orig:43 inHotKey$4+-3 ] [43])
> 	  (int_list:REG_BR_PROB 5000 (nil)))
>     -> 53)
>    (note 43 42 48 6 [bb 6] NOTE_INSN_BASIC_BLOCK)
>    (insn 48 43 47 6 (set (reg:SI 2 r2)
> 	  (mem/u/c:SI (reg:SI 1 r1) [4  S4 A32])) gcc/testsuite/g++.dg/torture/pr34651.C:22 7 {movsi_insn}
>         (expr_list:REG_DEAD (reg:SI 1 r1)
> 	  (nil)))
>    [...]
>    (code_label 53 169 54 7 6 "" [1 uses])
>    (note 54 53 12 7 [bb 7] NOTE_INSN_BASIC_BLOCK)
>    (insn 12 54 57 7 (set:SI (reg/f:SI 2 r2 [orig:46 D.2050 ] [46])
> 	  (mem/u/c:SI (reg:SI 1 r1) [4  S4 A32])) gcc/testsuite/g++.dg/torture/pr34651.C:22 7 {movsi_insn}
>         (expr_list:REG_DEAD (reg:SI 1 r1)
> 	  (expr_list:REG_EQUAL (symbol_ref/f:SI ("*.LC3") [flags 0x2]  <var_decl # *.LC3>)
> 	      (nil))))
>
> where insns 12 and 48 are identical except for the :SI on the SET.
> This difference prevents us from merging the heads of the two blocks;
> after removing it we replace the two loads with a single load before
> the branch.
>
> This patch removes the mode argument from gen_rtx_SET and updates
> all callers.  I used a script to (try to) make sure that all callers
> really had been caught.  I also built one target per CPU just in case.
> There were some changes in gcc.dg, g++.dg and gcc.c-torture assembly
> code for c6x-elf, lm32-elf and v850-elf, but all of them seemed to be
> code improvements from removing duplicated instructions.  (Other ports
> also passed spurious modes but apparently not in a way that affects
> the tests I'd tried.)  Also tested on x86_64-linux-gnu.  OK to install?
>
> BTW, I've split the patch up into two, the last bit being a mechanical
> removal of modes.  (I did it by hand though to try to keep things
> properly formatted.)
>
> Thanks,
> Richard
>
>
> gcc/
> 	* rtl.h (always_void_p): New function.
> 	* gengenrtl.c (always_void_p(: Likewise.
Typo in the ChangeLog.

non-mechanical part didn't seem to be attached.  I don't expect any 
problems there, but a quick looksie seems appropriate.

Mechanical bits are obviously OK once the non-mechanical bits are in place.

jeff