* Helpers:
Using the tcg_gen_helper_x_y it is possible to call any function
-taking i32, i64 or pointer types. By default, before calling an helper,
+taking i32, i64 or pointer types. By default, before calling a helper,
all globals are stored at their canonical location and it is assumed
-that the function can modify them. This can be overriden by the
+that the function can modify them. This can be overridden by the
TCG_CALL_CONST function modifier. By default, the helper is allowed to
-modify the CPU state or raise an exception. This can be overriden by
+modify the CPU state or raise an exception. This can be overridden by
the TCG_CALL_PURE function modifier, in which case the call to the
function is removed if the return value is not used.
Indicate that the value of t0 won't be used later. It is useful to
force dead code elimination.
+* deposit_i32/i64 dest, t1, t2, pos, len
+
+Deposit T2 as a bitfield into T1, placing the result in DEST.
+The bitfield is described by POS/LEN, which are immediate values:
+
+ LEN - the length of the bitfield
+ POS - the position of the first bit, counting from the LSB
+
+For example, pos=8, len=4 indicates a 4-bit field at bit 8.
+This operation would be equivalent to
+
+ dest = (t1 & ~0x0f00) | ((t2 << 8) & 0x0f00)
+
+
********* Conditional moves
* setcond_i32/i64 cond, dest, t1, t2
********* QEMU specific operations
-* tb_exit t0
+* exit_tb t0
Exit the current TB and return the value t0 (word type).
the speed of the translation.
- Don't hesitate to use helpers for complicated or seldom used target
- intructions. There is little performance advantage in using TCG to
+ instructions. There is little performance advantage in using TCG to
implement target instructions taking more than about twenty TCG
- instructions.
+ instructions. Note that this rule of thumb is more applicable to
+ helpers doing complex logic or arithmetic, where the C compiler has
+ scope to do a good job of optimisation; it is less relevant where
+ the instruction is mostly doing loads and stores, and in those cases
+ inline TCG may still be faster for longer sequences.
+
+- The hard limit on the number of TCG instructions you can generate
+ per target instruction is set by MAX_OP_PER_INSTR in exec-all.h --
+ you cannot exceed this without risking a buffer overrun.
- Use the 'discard' instruction if you know that TCG won't be able to
prove that a given global is "dead" at a given program point. The