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| author | Paolo Bonzini <pbonzini@redhat.com> | 2016-10-06 15:10:57 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-10-07 10:05:22 +0200 |
| commit | c3ce5a235741cb027b1328288ddec06470254813 (patch) | |
| tree | 18b91ded381a74e17158c282dea2047b0ae3c3e6 /target-s390x | |
| parent | bf28a69eeb53e9e45166fbdda032454e7b1e3f29 (diff) | |
| download | qemu-c3ce5a235741cb027b1328288ddec06470254813.tar.gz qemu-c3ce5a235741cb027b1328288ddec06470254813.tar.bz2 qemu-c3ce5a235741cb027b1328288ddec06470254813.zip | |
qemu-tech: document lazy condition code evaluation in cpu.h
Unlike the other sections, they are pretty specific to a particular CPU.
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'target-s390x')
| -rw-r--r-- | target-s390x/cpu.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h index 4fb34b598d..4e58cdee3e 100644 --- a/target-s390x/cpu.h +++ b/target-s390x/cpu.h @@ -671,6 +671,13 @@ ObjectClass *s390_cpu_class_by_name(const char *name); /* CC optimization */ +/* Instead of computing the condition codes after each x86 instruction, + * QEMU just stores the result (called CC_DST), the type of operation + * (called CC_OP) and whatever operands are needed (CC_SRC and possibly + * CC_VR). When the condition codes are needed, the condition codes can + * be calculated using this information. Condition codes are not generated + * if they are only needed for conditional branches. + */ enum cc_op { CC_OP_CONST0 = 0, /* CC is 0 */ CC_OP_CONST1, /* CC is 1 */ |