9b2bd54c98edb185a3985410367754ab33217362bnicholesTiny Code Generator - Fabrice Bellard.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes1) Introduction

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesTCG (Tiny Code Generator) began as a generic backend for a C

9b2bd54c98edb185a3985410367754ab33217362bnicholescompiler. It was simplified to be used in QEMU. It also has its roots

9b2bd54c98edb185a3985410367754ab33217362bnicholesin the QOP code generator written by Paul Brook.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes2) Definitions

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesThe TCG "target" is the architecture for which we generate the

9b2bd54c98edb185a3985410367754ab33217362bnicholescode. It is of course not the same as the "target" of QEMU which is

9b2bd54c98edb185a3985410367754ab33217362bnicholesthe emulated architecture. As TCG started as a generic C backend used

9b2bd54c98edb185a3985410367754ab33217362bnicholesfor cross compiling, it is assumed that the TCG target is different

9b2bd54c98edb185a3985410367754ab33217362bnicholesfrom the host, although it is never the case for QEMU.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesA TCG "function" corresponds to a QEMU Translated Block (TB).

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesA TCG "temporary" is a variable only live in a basic

9b2bd54c98edb185a3985410367754ab33217362bnicholesblock. Temporaries are allocated explicitly in each function.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesA TCG "local temporary" is a variable only live in a function. Local

70953fb44a7140fe206c3a5f011e24209c8c5c6abnicholestemporaries are allocated explicitly in each function.

70953fb44a7140fe206c3a5f011e24209c8c5c6abnicholes

70953fb44a7140fe206c3a5f011e24209c8c5c6abnicholesA TCG "global" is a variable which is live in all the functions

9b2bd54c98edb185a3985410367754ab33217362bnicholes(equivalent of a C global variable). They are defined before the

9b2bd54c98edb185a3985410367754ab33217362bnicholesfunctions defined. A TCG global can be a memory location (e.g. a QEMU

9b2bd54c98edb185a3985410367754ab33217362bnicholesCPU register), a fixed host register (e.g. the QEMU CPU state pointer)

9b2bd54c98edb185a3985410367754ab33217362bnicholesor a memory location which is stored in a register outside QEMU TBs

9b2bd54c98edb185a3985410367754ab33217362bnicholes(not implemented yet).

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesA TCG "basic block" corresponds to a list of instructions terminated

9b2bd54c98edb185a3985410367754ab33217362bnicholesby a branch instruction.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes3) Intermediate representation

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes3.1) Introduction

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesTCG instructions operate on variables which are temporaries, local

9b2bd54c98edb185a3985410367754ab33217362bnicholestemporaries or globals. TCG instructions and variables are strongly

9b2bd54c98edb185a3985410367754ab33217362bnicholestyped. Two types are supported: 32 bit integers and 64 bit

9b2bd54c98edb185a3985410367754ab33217362bnicholesintegers. Pointers are defined as an alias to 32 bit or 64 bit

9b2bd54c98edb185a3985410367754ab33217362bnicholesintegers depending on the TCG target word size.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesEach instruction has a fixed number of output variable operands, input

9b2bd54c98edb185a3985410367754ab33217362bnicholesvariable operands and always constant operands.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesThe notable exception is the call instruction which has a variable

9b2bd54c98edb185a3985410367754ab33217362bnicholesnumber of outputs and inputs.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesIn the textual form, output operands usually come first, followed by

9b2bd54c98edb185a3985410367754ab33217362bnicholesinput operands, followed by constant operands. The output type is

9b2bd54c98edb185a3985410367754ab33217362bnicholesincluded in the instruction name. Constants are prefixed with a '$'.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesadd_i32 t0, t1, t2 (t0 <- t1 + t2)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes3.2) Assumptions

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* Basic blocks

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg- Basic blocks end after branches (e.g. brcond_i32 instruction),

9b2bd54c98edb185a3985410367754ab33217362bnicholes goto_tb and exit_tb instructions.

9b2bd54c98edb185a3985410367754ab33217362bnicholes- Basic blocks start after the end of a previous basic block, or at a

9b2bd54c98edb185a3985410367754ab33217362bnicholes set_label instruction.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesAfter the end of a basic block, the content of temporaries is

9b2bd54c98edb185a3985410367754ab33217362bnicholesdestroyed, but local temporaries and globals are preserved.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* Floating point types are not supported yet

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* Pointers: depending on the TCG target, pointer size is 32 bit or 64

9b2bd54c98edb185a3985410367754ab33217362bnicholes bit. The type TCG_TYPE_PTR is an alias to TCG_TYPE_I32 or

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_TYPE_I64.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg* Helpers:

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesUsing the tcg_gen_helper_x_y it is possible to call any function

9b2bd54c98edb185a3985410367754ab33217362bnicholestaking i32, i64 or pointer types. By default, before calling an helper,

9b2bd54c98edb185a3985410367754ab33217362bnicholesall globals are stored at their canonical location and it is assumed

9b2bd54c98edb185a3985410367754ab33217362bnicholesthat the function can modify them. This can be overriden by the

9b2bd54c98edb185a3985410367754ab33217362bnicholesTCG_CALL_CONST function modifier. By default, the helper is allowed to

9b2bd54c98edb185a3985410367754ab33217362bnicholesmodify the CPU state or raise an exception. This can be overriden by

9b2bd54c98edb185a3985410367754ab33217362bnicholesthe TCG_CALL_PURE function modifier, in which case the call to the

9b2bd54c98edb185a3985410367754ab33217362bnicholesfunction is removed if the return value is not used.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesOn some TCG targets (e.g. x86), several calling conventions are

9b2bd54c98edb185a3985410367754ab33217362bnicholessupported.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* Branches:

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesUse the instruction 'br' to jump to a label. Use 'jmp' to jump to an

9b2bd54c98edb185a3985410367754ab33217362bnicholesexplicit address. Conditional branches can only jump to labels.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes3.3) Code Optimizations

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesWhen generating instructions, you can count on at least the following

ac7985784d08a3655291f24f711812b4d8b1cbcffuankgoptimizations:

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes- Single instructions are simplified, e.g.

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholes and_i32 t0, t0, $0xffffffff

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes is suppressed.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes- A liveness analysis is done at the basic block level. The

9b2bd54c98edb185a3985410367754ab33217362bnicholes information is used to suppress moves from a dead variable to

9b2bd54c98edb185a3985410367754ab33217362bnicholes another one. It is also used to remove instructions which compute

9b2bd54c98edb185a3985410367754ab33217362bnicholes dead results. The later is especially useful for condition code

9b2bd54c98edb185a3985410367754ab33217362bnicholes optimization in QEMU.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes In the following example:

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholes add_i32 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes add_i32 t0, t0, $1

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg mov_i32 t0, $1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes only the last instruction is kept.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes3.4) Instruction Reference

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes********* Function call

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* call <ret> <params> ptr

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholescall function 'ptr' (pointer type)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes<ret> optional 32 bit or 64 bit return value

9b2bd54c98edb185a3985410367754ab33217362bnicholes<params> optional 32 bit or 64 bit parameters

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes********* Jumps/Labels

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* jmp t0

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesAbsolute jump to address t0 (pointer type).

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* set_label $label

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesDefine label 'label' at the current program point.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* br $label

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholesJump to label.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg* brcond_i32/i64 cond, t0, t1, label

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesConditional jump if t0 cond t1 is true. cond can be:

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_EQ

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg TCG_COND_NE

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_LT /* signed */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_GE /* signed */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_LE /* signed */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_GT /* signed */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_LTU /* unsigned */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_GEU /* unsigned */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_LEU /* unsigned */

9b2bd54c98edb185a3985410367754ab33217362bnicholes TCG_COND_GTU /* unsigned */

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes********* Arithmetic

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* add_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1+t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* sub_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1-t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

bf1e7c075ccc3e6597d17de7641332ff6ff92e8astriker* neg_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=-t1 (two's complement)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* mul_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1*t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* div_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankgt0=t1/t2 (signed). Undefined behavior if division by zero or overflow.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* divu_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1/t2 (unsigned). Undefined behavior if division by zero.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* rem_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1%t2 (signed). Undefined behavior if division by zero or overflow.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* remu_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1%t2 (unsigned). Undefined behavior if division by zero.

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes********* Logical

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* and_i32/i64 t0, t1, t2

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1&t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* or_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1|t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* xor_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1^t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* not_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=~t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* andc_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1&~t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* eqv_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=~(t1^t2), or equivalently, t0=t1^~t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

25ca39766f78dd95d6cda08262cfdd76a18be8b6bnicholes* nand_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=~(t1&t2)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* nor_i32/i64 t0, t1, t2

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

609ef720afd62ca63391c9fdb415cd2faf29aa46bnicholest0=~(t1|t2)

609ef720afd62ca63391c9fdb415cd2faf29aa46bnicholes

609ef720afd62ca63391c9fdb415cd2faf29aa46bnicholes* orc_i32/i64 t0, t1, t2

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

609ef720afd62ca63391c9fdb415cd2faf29aa46bnicholest0=t1|~t2

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg********* Shifts/Rotates

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* shl_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1 << t2. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg* shr_i32/i64 t0, t1, t2

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholest0=t1 >> t2 (unsigned). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* sar_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankgt0=t1 >> t2 (signed). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* rotl_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesRotation of t2 bits to the left. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* rotr_i32/i64 t0, t1, t2

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesRotation of t2 bits to the right. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes********* Misc

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg

9b2bd54c98edb185a3985410367754ab33217362bnicholes* mov_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholest0 = t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholesMove t1 to t0 (both operands must have the same type).

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* ext8s_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholesext8u_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholesext16s_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholesext16u_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholesext32s_i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholesext32u_i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes8, 16 or 32 bit sign/zero extension (both operands must have the same type)

9b2bd54c98edb185a3985410367754ab33217362bnicholes

9b2bd54c98edb185a3985410367754ab33217362bnicholes* bswap16_i32/i64 t0, t1

9b2bd54c98edb185a3985410367754ab33217362bnicholes

ac7985784d08a3655291f24f711812b4d8b1cbcffuankg16 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, it assumes that

the four high order bytes are set to zero.

* bswap64_i64 t0, t1

64 bit byte swap

* discard_i32/i64 t0

Indicate that the value of t0 won't be used later. It is useful to

force dead code elimination.

********* Conditional moves

* setcond_i32/i64 cond, dest, t1, t2

dest = (t1 cond t2)

Set DEST to 1 if (T1 cond T2) is true, otherwise set to 0.

********* Type conversions

* ext_i32_i64 t0, t1

Convert t1 (32 bit) to t0 (64 bit) and does sign extension

* extu_i32_i64 t0, t1

Convert t1 (32 bit) to t0 (64 bit) and does zero extension

* trunc_i64_i32 t0, t1

Truncate t1 (64 bit) to t0 (32 bit)

* concat_i32_i64 t0, t1, t2

Construct t0 (64-bit) taking the low half from t1 (32 bit) and the high half

from t2 (32 bit).

* concat32_i64 t0, t1, t2

Construct t0 (64-bit) taking the low half from t1 (64 bit) and the high half

from t2 (64 bit).

********* Load/Store

* ld_i32/i64 t0, t1, offset

ld8s_i32/i64 t0, t1, offset

ld8u_i32/i64 t0, t1, offset

ld16s_i32/i64 t0, t1, offset

ld16u_i32/i64 t0, t1, offset

ld32s_i64 t0, t1, offset

ld32u_i64 t0, t1, offset

t0 = read(t1 + offset)

Load 8, 16, 32 or 64 bits with or without sign extension from host memory.

offset must be a constant.

* st_i32/i64 t0, t1, offset

st8_i32/i64 t0, t1, offset

st16_i32/i64 t0, t1, offset

st32_i64 t0, t1, offset

write(t0, t1 + offset)

Write 8, 16, 32 or 64 bits to host memory.

********* 64-bit target on 32-bit host support

The following opcodes are internal to TCG. Thus they are to be implemented by

32-bit host code generators, but are not to be emitted by guest translators.

They are emitted as needed by inline functions within "tcg-op.h".

* brcond2_i32 cond, t0_low, t0_high, t1_low, t1_high, label

Similar to brcond, except that the 64-bit values T0 and T1

are formed from two 32-bit arguments.

* add2_i32 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high

* sub2_i32 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high

Similar to add/sub, except that the 64-bit inputs T1 and T2 are

formed from two 32-bit arguments, and the 64-bit output T0

is returned in two 32-bit outputs.

* mulu2_i32 t0_low, t0_high, t1, t2

Similar to mul, except two 32-bit (unsigned) inputs T1 and T2 yielding

the full 64-bit product T0. The later is returned in two 32-bit outputs.

* setcond2_i32 cond, dest, t1_low, t1_high, t2_low, t2_high

Similar to setcond, except that the 64-bit values T1 and T2 are

formed from two 32-bit arguments. The result is a 32-bit value.

********* QEMU specific operations

* tb_exit t0

Exit the current TB and return the value t0 (word type).

* goto_tb index

Exit the current TB and jump to the TB index 'index' (constant) if the

current TB was linked to this TB. Otherwise execute the next

instructions.

* qemu_ld8u t0, t1, flags

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.

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

qemu_st32 t0, t1, flags

qemu_st64 t0, t1, flags

Store the data t0 at the QEMU CPU Address t1. t1 has the QEMU CPU

address type. 'flags' contains the QEMU memory index (selects user or

kernel access) for example.

Note 1: Some shortcuts are defined when the last operand is known to be

a constant (e.g. addi for add, movi for mov).

Note 2: When using TCG, the opcodes must never be generated directly

as some of them may not be available as "real" opcodes. Always use the

function tcg_gen_xxx(args).

4) Backend

tcg-target.h contains the target specific definitions. tcg-target.c

contains the target specific code.

4.1) Assumptions

The target word size (TCG_TARGET_REG_BITS) is expected to be 32 bit or

64 bit. It is expected that the pointer has the same size as the word.

On a 32 bit target, all 64 bit operations are converted to 32 bits. A

few specific operations must be implemented to allow it (see add2_i32,

sub2_i32, brcond2_i32).

Floating point operations are not supported in this version. A

previous incarnation of the code generator had full support of them,

but it is better to concentrate on integer operations first.

On a 64 bit target, no assumption is made in TCG about the storage of

the 32 bit values in 64 bit registers.

4.2) Constraints

GCC like constraints are used to define the constraints of every

instruction. Memory constraints are not supported in this

version. Aliases are specified in the input operands as for GCC.

The same register may be used for both an input and an output, even when

they are not explicitly aliased. If an op expands to multiple target

instructions then care must be taken to avoid clobbering input values.

GCC style "early clobber" outputs are not currently supported.

A target can define specific register or constant constraints. If an

operation uses a constant input constraint which does not allow all

constants, it must also accept registers in order to have a fallback.

The movi_i32 and movi_i64 operations must accept any constants.

The mov_i32 and mov_i64 operations must accept any registers of the

same type.

The ld/st instructions must accept signed 32 bit constant offsets. It

can be implemented by reserving a specific register to compute the

address if the offset is too big.

The ld/st instructions must accept any destination (ld) or source (st)

register.

4.3) Function call assumptions

- The only supported types for parameters and return value are: 32 and

64 bit integers and pointer.

- The stack grows downwards.

- The first N parameters are passed in registers.

- The next parameters are passed on the stack by storing them as words.

- Some registers are clobbered during the call.

- The function can return 0 or 1 value in registers. On a 32 bit

target, functions must be able to return 2 values in registers for

64 bit return type.

5) Recommended coding rules for best performance

- Use globals to represent the parts of the QEMU CPU state which are

often modified, e.g. the integer registers and the condition

codes. TCG will be able to use host registers to store them.

- Avoid globals stored in fixed registers. They must be used only to

store the pointer to the CPU state and possibly to store a pointer

to a register window.

- Use temporaries. Use local temporaries only when really needed,

e.g. when you need to use a value after a jump. Local temporaries

introduce a performance hit in the current TCG implementation: their

content is saved to memory at end of each basic block.

- Free temporaries and local temporaries when they are no longer used

(tcg_temp_free). Since tcg_const_x() also creates a temporary, you

should free it after it is used. Freeing temporaries does not yield

a better generated code, but it reduces the memory usage of TCG and

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

implement target instructions taking more than about twenty TCG

instructions.

- 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

x86 target uses it to improve the condition codes optimisation.