Messages in this thread | | | Date | Thu, 24 Mar 2016 15:36:39 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/2] include/linux: apply __malloc attribute |
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On Thu, 24 Mar 2016 00:42:32 +0100 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:
> Attach the malloc attribute to a few allocation functions. This helps > gcc generate better code by telling it that the return value doesn't > alias any existing pointers (which is even more valuable given the > pessimizations implied by -fno-strict-aliasing). > > A simple example of what this allows gcc to do can be seen by looking > at the last part of drm_atomic_helper_plane_reset: > > plane->state = kzalloc(sizeof(*plane->state), GFP_KERNEL); > > if (plane->state) { > plane->state->plane = plane; > plane->state->rotation = BIT(DRM_ROTATE_0); > } > > which compiles to > > e8 99 bf d6 ff callq ffffffff8116d540 <kmem_cache_alloc_trace> > 48 85 c0 test %rax,%rax > 48 89 83 40 02 00 00 mov %rax,0x240(%rbx) > 74 11 je ffffffff814015c4 <drm_atomic_helper_plane_reset+0x64> > 48 89 18 mov %rbx,(%rax) > 48 8b 83 40 02 00 00 mov 0x240(%rbx),%rax [*] > c7 40 40 01 00 00 00 movl $0x1,0x40(%rax) > > With this patch applied, the instruction at [*] is elided, since the > store to plane->state->plane is known to not alter the value of > plane->state.
Shaves 6 bytes off my 1MB i386 defconfig vmlinux. Winner!
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