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>
@menu
* QEMU compared to other emulators::
* Portable dynamic translation::
-* Condition code optimisations::
* CPU state optimisations::
* Translation cache::
* Direct block chaining::
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
void cris_initialize_tcg(void);
void cris_initialize_crisv10_tcg(void);
+/* Instead of computing the condition codes after each CRIS instruction,
+ * QEMU just stores one operand (called CC_SRC), the result
+ * (called CC_DEST) 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.
+ */
enum {
CC_OP_DYNAMIC, /* Use env->cc_op */
CC_OP_FLAGS,
/* Use a clearer name for this. */
#define CPU_INTERRUPT_INIT CPU_INTERRUPT_RESET
+/* 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 */
void *puc);
void cpu_m68k_flush_flags(CPUM68KState *, int);
+
+/* Instead of computing the condition codes after each m68k instruction,
+ * QEMU just stores one operand (called CC_SRC), the result
+ * (called CC_DEST) 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.
+ */
enum {
CC_OP_DYNAMIC, /* Use env->cc_op */
CC_OP_FLAGS, /* CC_DEST = CVZN, CC_SRC = unused */
/* 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 */
#define CC_DST (env->cc_dst)
#define CC_OP (env->cc_op)
+/* Even though lazy evaluation of CPU condition codes tends to be less
+ * important on RISC systems where condition codes are only updated
+ * when explicitly requested, SPARC uses it to update 32-bit and 64-bit
+ * condition codes.
+ */
enum {
CC_OP_DYNAMIC, /* must use dynamic code to get cc_op */
CC_OP_FLAGS, /* all cc are back in status register */