path: root/target-i386
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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 /target-i386
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 'target-i386')
1 files changed, 7 insertions, 0 deletions
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 1cb32ae456..e64569854f 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -698,6 +698,13 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
/* Use a clearer name for this. */
+/* Instead of computing the condition codes after each x86 instruction,
+ * QEMU just stores one operand (called CC_SRC), the result
+ * (called CC_DST) and the type of operation (called CC_OP). 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.
+ */
typedef enum {
CC_OP_DYNAMIC, /* must use dynamic code to get cc_op */
CC_OP_EFLAGS, /* all cc are explicitly computed, CC_SRC = flags */