User Guide for R600 Back-end — LLVM 3.7 documentation

# User Guide for R600 Back-end

## Introduction

The R600 back-end provides ISA code generation for AMD GPUs, starting with the R600 family up until the current Volcanic Islands (GCN Gen 3).

## Assembler

The assembler is currently considered experimental.

For syntax examples look in test/MC/R600.

Below some of the currently supported features (modulo bugs). These all apply to the Southern Islands ISA, Sea Islands and Volcanic Islands are also supported but may be missing some instructions and have more bugs:

### DS Instructions

All DS instructions are supported.

### MUBUF Instructions

All non-atomic MUBUF instructions are supported.

### SMRD Instructions

Only the s_load_dword* SMRD instructions are supported.

### SOP1 Instructions

All SOP1 instructions are supported.

### SOP2 Instructions

All SOP2 instructions are supported.

### SOPC Instructions

All SOPC instructions are supported.

### SOPP Instructions

Unless otherwise mentioned, all SOPP instructions that have one or more operands accept integer operands only. No verification is performed on the operands, so it is up to the programmer to be familiar with the range or acceptable values.

#### s_waitcnt

s_waitcnt accepts named arguments to specify which memory counter(s) to wait for.

    // Wait for all counters to be 0
    s_waitcnt 0

    // Equivalent to s_waitcnt 0.  Counter names can also be delimited by
    // '&' or ','.
    s_waitcnt vmcnt(0) expcnt(0) lgkcmt(0)

    // Wait for vmcnt counter to be 1.
    s_waitcnt vmcnt(1)

### VOP1, VOP2, VOP3, VOPC Instructions

All 32-bit and 64-bit encodings should work.

The assembler will automatically detect which encoding size to use for VOP1, VOP2, and VOPC instructions based on the operands. If you want to force a specific encoding size, you can add an _e32 (for 32-bit encoding) or _e64 (for 64-bit encoding) suffix to the instruction. Most, but not all instructions support an explicit suffix. These are all valid assembly strings:

    v_mul_i32_i24 v1, v2, v3
    v_mul_i32_i24_e32 v1, v2, v3
    v_mul_i32_i24_e64 v1, v2, v3