Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [discuss] [PATCH] x86-64: memset optimization | Date | Sun, 19 Aug 2007 20:24:24 +0200 |
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> I am looking at current source, built with current (non-experimental) GCC > from Fedora Core 7. If I dissassemble ether_setup, which is > > void ether_setup(struct net_device *dev) > { > ... > > memset(dev->broadcast, 0xFF, ETH_ALEN); > } > > I see a tail recursion (jmp) to memset which is the code in arch/x86_64/lib/memset.S
That is likely gcc then deciding it can't use an inline memset for some reason. It does that for example if it can't figure out the alignment or similar. Honza (cc'ed) can probably give you more details why it happens, especially if you give him a preprocessed self contained test case.
A simple example like char x[6];
f() { memset(x, 1, 6); }
gives with gcc 4.1:
.text .p2align 4,,15 .globl f .type f, @function f: .LFB2: movl $16843009, x(%rip) movw $257, x+4(%rip) ret .LFE2:
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