DOS ain't dead

CMOV (Developers)

posted by ecm , Düsseldorf, Germany, 22.03.2020, 14:26

> (P6 has a highly useful cmov that reduces branching, and is a substitute
> for a branch instruction and a mov. IIRC it is 3 bytes and replaces a one
> byte branch and two bytes mov. (in both cases + size of imm), equal size,
> better performance)

I recently discussed whether CMOVcc is available in all AMD64 processors: https://stackoverflow.com/questions/60760138/do-al...mplementations-support-the-cmovcc-instructions/

The other answer of mine linked from there includes this statement about CMOVcc:

> (I came across this thread involving Linus Torvalds which indicates that the conditional jump solution may actually be better or no worse than cmov. Make of that what you will.)

Note that CMOVcc has its own CPUID support bit. A processor being a 686+ class does not necessarily mean it has CMOVcc.

---
l

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Complete thread:

rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - Rugxulo, 14.03.2020, 08:13 (Developers)
- rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - Rugxulo, 16.03.2020, 01:24
  - rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - rr, 16.03.2020, 15:22
    - rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 17.03.2020, 05:20
      - rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 17.03.2020, 06:58
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 22.03.2020, 00:48
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 22.03.2020, 10:13
        rebuilding NASM 2.09 and NASM compatibility - ecm, 22.03.2020, 11:45
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 06.09.2020, 23:09
      - rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 22.03.2020, 00:42
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - marcov, 22.03.2020, 13:08
        CMOV - ecm, 22.03.2020, 14:26
        CMOV - marcov, 22.03.2020, 18:32
        CMOV - marcov, 23.03.2020, 12:52
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 23.03.2020, 04:27
        NASM 0.98.39 (MSC 7, "286", not full instruction support) - Rugxulo, 24.03.2020, 20:36
        NASM 0.98.39 (not full instruction support) - Rugxulo, 24.03.2020, 21:16
        NASM 0.98.39 (not full instruction support) - ecm, 24.03.2020, 22:55
        NASM 0.98.39 (not full instruction support) - Rugxulo, 24.03.2020, 23:17
        NASM 0.98.39 (not full instruction support) ... LOADALL - Rugxulo, 31.03.2020, 20:07
        rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 13.04.2020, 07:16
        deprecated MMX and obsolete 3DNow! - Rugxulo, 24.03.2020, 17:54