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Visual C++ 2008 producing very strange code

Joe Black · 2008-08-03T12:50:58

I was looking at some assembler output and I noticed the following: This line of code (a and b are floats) return a < b ? a : b; creates the following output movss xmm0, DWORD PTR _a$[esp+8] movss xmm1, DWORD PTR _b$[esp+8] cvtps2pd xmm0, xmm0 cvtps2pd xmm1, xmm1 comisd xmm1, xmm0 lea eax, DWORD PTR _a$[esp+8] ja SHORT $LN6@main lea eax, DWORD PTR _b$[esp+8] $LN6@main: I find it very strange that two single-precision floats are first expanded into double precision floats before being compared. Why isn't comiss used instead of comisd? This would save two instructions and would generally seem to be far more efficient.

General and Gameplay Programming Programming

Started by l0calh05t August 02, 2008 02:53 PM

18 comments, last by l0calh05t 15 years, 8 months ago

l0calh05t

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August 03, 2008 12:50 PM

Quote:If you use Linux you can continue using the Intel C++ compiler for non-commercial use.

Thanks for the hint, but when I'm not using Windows I'm using FreeBSD. I've been thinking about buying a student license (much cheaper) but I couldn't find any details on the license terms...

Visual C++ 2008 producing very strange code

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Visual C++ 2008 producing very strange code

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