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Re: arm memcpy of aligned data


On 28 May 2015, at 23:15, Mike Stump <mikestump@comcast.net> wrote:

> So, the arm memcpy code of aligned data isn’t as good as it can be.
> 
> void *memcpy(void *dest, const void *src, unsigned int n);
> 
> void foo(char *dst, int i) {
>  memcpy (dst, &i, sizeof (i));
> }
> 
> generates horrible code, but, it we are willing to notice the src or the destination are aligned, we can do much better:
> 

This looks like PR 50417, doesn't it?

Cheers,
Oleg





> $ ./cc1 -fschedule-fusion -fdump-tree-all-all -da -march=armv7ve -mcpu=cortex-m4 -fomit-frame-pointer -quiet -O2 /tmp/t.c -o t.s
> $ cat t.s
> [ … ]
> foo:
> 	@ args = 0, pretend = 0, frame = 4
> 	@ frame_needed = 0, uses_anonymous_args = 0
> 	@ link register save eliminated.
> 	sub	sp, sp, #4
> 	str	r1, [r0]	@ unaligned
> 	add	sp, sp, #4
> 
> Index: gcc/config/arm/arm.c
> ===================================================================
> --- gcc/config/arm/arm.c	(revision 223842)
> +++ gcc/config/arm/arm.c	(working copy)
> @@ -14376,7 +14376,10 @@ arm_block_move_unaligned_straight (rtx d
> 				srcoffset + j * UNITS_PER_WORD - src_autoinc);
> 	  mem = adjust_automodify_address (srcbase, SImode, addr,
> 					   srcoffset + j * UNITS_PER_WORD);
> -	  emit_insn (gen_unaligned_loadsi (regs[j], mem));
> +	  if (src_aligned)
> +	    emit_move_insn (regs[j], mem);
> +	  else
> +	    emit_insn (gen_unaligned_loadsi (regs[j], mem));
> 	}
>       srcoffset += words * UNITS_PER_WORD;
>     }
> @@ -14395,7 +14398,10 @@ arm_block_move_unaligned_straight (rtx d
> 				dstoffset + j * UNITS_PER_WORD - dst_autoinc);
> 	  mem = adjust_automodify_address (dstbase, SImode, addr,
> 					   dstoffset + j * UNITS_PER_WORD);
> -	  emit_insn (gen_unaligned_storesi (mem, regs[j]));
> +	  if (dst_aligned)
> +	    emit_move_insn (mem, regs[j]);
> +	  else
> +	    emit_insn (gen_unaligned_storesi (mem, regs[j]));
> 	}
>       dstoffset += words * UNITS_PER_WORD;
>     }
> 
> 
> Ok?
> 
> Can someone spin this through an arm test suite run for me, I was doing this by inspection and cross compile on a system with no arm bits.  Bonus points if you can check it in with the test case above marked up as appropriate.
> 
> <arm.diffs.txt>


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