问题
I am trying to run various benchmark tests using CPU2006 to see what various optimizations do in terms of speed on gcc. I am familiar with -O1, -O2, and -O3, but have heard that -msse is a decent optimization. What exactly is -msse? I've also seen that -msse is default on a 64 bit architecture, so how do I disable it to compare the difference between using it and not using it?
回答1:
http://www.justskins.com/forums/gcc-option-msse-and-128289.html
SSE (http://it.wikipedia.org/wiki/Streaming_SIMD_Extensions) as the name says are the SSE instructions present in processors since Pentium 3. They are fast for some kind of vectorial and floating point computation. They are available in all 64 bit processors, so why should we disable them?
You can choose between -msse and -msse2. SSE2 are another instruction set built over SSE that add other powerful and very fast vectorial instructions.
Pentium 3 did have SSE, and is a 32 bit processor. SSE2 is more modern instead, Pentium 4, that is still a 32 bit processor, have SSE2.
回答2:
-msse activates the generation of SSE instructions. All 64-bit processors (x86-64) have them, but some older 32-bit processors (IA-32) do not have these instructions. This is the reason for GCC's default settings.
SSE instructions have to do with vector operations and floating-point. Considering that opportunities for automatic vectorization are rare in general-purpose code, the only difference you are likely to observe are if you use floating-point.
On 64-bit, to disable SSE instructions, use -mno-sse
来源：https://stackoverflow.com/questions/7894633/disabling-msse