* 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.
* bswap16_i32/i64 t0, t1
-16 bit byte swap on a 32/64 bit value. The two/six high order bytes must be
-set to zero.
+16 bit byte swap on a 32/64 bit value. It assumes that the two/six high order
+bytes are set to zero.
* bswap32_i32/i64 t0, t1
-32 bit byte swap on a 32/64 bit value. With a 64 bit value, the four high
-order bytes must be set to zero.
+32 bit byte swap on a 32/64 bit value. With a 64 bit value, it assumes that
+the four high order bytes are set to zero.
* bswap64_i64 t0, t1
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).
qemu_ld8s t0, t1, flags
qemu_ld16u t0, t1, flags
qemu_ld16s t0, t1, flags
+qemu_ld32 t0, t1, flags
qemu_ld32u t0, t1, flags
qemu_ld32s t0, t1, flags
qemu_ld64 t0, t1, flags
-Load data at the QEMU CPU address t1 into t0. t1 has the QEMU CPU
-address type. 'flags' contains the QEMU memory index (selects user or
-kernel access) for example.
+Load data at the QEMU CPU address t1 into t0. t1 has the QEMU CPU address
+type. 'flags' contains the QEMU memory index (selects user or kernel access)
+for example.
+
+Note that "qemu_ld32" implies a 32-bit result, while "qemu_ld32u" and
+"qemu_ld32s" imply a 64-bit result appropriately extended from 32 bits.
* qemu_st8 t0, t1, flags
qemu_st16 t0, t1, flags
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
projects / qemu.git / blobdiff