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authorPaolo Bonzini <pbonzini@redhat.com>2016-10-06 15:10:57 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2016-10-07 10:05:22 +0200
commitc3ce5a235741cb027b1328288ddec06470254813 (patch)
tree18b91ded381a74e17158c282dea2047b0ae3c3e6 /qemu-tech.texi
parentbf28a69eeb53e9e45166fbdda032454e7b1e3f29 (diff)
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 'qemu-tech.texi')
-rw-r--r--qemu-tech.texi25
1 files changed, 0 insertions, 25 deletions
diff --git a/qemu-tech.texi b/qemu-tech.texi
index 082b62c8e0..75ceea408c 100644
--- a/qemu-tech.texi
+++ b/qemu-tech.texi
@@ -214,7 +214,6 @@ SH4
@menu
* QEMU compared to other emulators::
* Portable dynamic translation::
-* Condition code optimisations::
* CPU state optimisations::
* Translation cache::
* Direct block chaining::
@@ -290,30 +289,6 @@ performances.
QEMU's dynamic translation backend is called TCG, for "Tiny Code
Generator". For more information, please take a look at @code{tcg/README}.
-@node Condition code optimisations
-@section Condition code optimisations
-
-Lazy evaluation of CPU condition codes (@code{EFLAGS} register on x86)
-is important for CPUs where every instruction sets the condition
-codes. It tends to be less important on conventional RISC systems
-where condition codes are only updated when explicitly requested. On
-Sparc64, costly update of both 32 and 64 bit condition codes can be
-avoided with lazy evaluation.
-
-Instead of computing the condition codes after each x86 instruction,
-QEMU just stores one operand (called @code{CC_SRC}), the result
-(called @code{CC_DST}) and the type of operation (called
-@code{CC_OP}). When the condition codes are needed, the condition
-codes can be calculated using this information. In addition, an
-optimized calculation can be performed for some instruction types like
-conditional branches.
-
-@code{CC_OP} is almost never explicitly set in the generated code
-because it is known at translation time.
-
-The lazy condition code evaluation is used on x86, m68k, cris and
-Sparc. ARM uses a simplified variant for the N and Z flags.
-
@node CPU state optimisations
@section CPU state optimisations