Xtensa Immediate Relaxation (Using as)

9.55.4.4 Other Immediate Field Relaxation

The assembler normally performs the following other relaxations. They can be disabled by using underscore prefixes (see Opcode Names), the --no-transform command-line option (see Command-line Options), or the no-transform directive (see transform).

The MOVI machine instruction can only materialize values in the range from -2048 to 2047. Values outside this range are best materialized with L32R instructions. Thus:

    movi a0, 100000

is assembled into the following machine code:

    .literal .L1, 100000
    l32r a0, .L1

The L8UI machine instruction can only be used with immediate offsets in the range from 0 to 255. The L16SI and L16UI machine instructions can only be used with offsets from 0 to 510. The L32I machine instruction can only be used with offsets from 0 to 1020. A load offset outside these ranges can be materialized with an L32R instruction if the destination register of the load is different than the source address register. For example:

    l32i a1, a0, 2040

is translated to:

    .literal .L1, 2040
    l32r a1, .L1

    add a1, a0, a1
    l32i a1, a1, 0

If the load destination and source address register are the same, an out-of-range offset causes an error.

The Xtensa ADDI instruction only allows immediate operands in the range from -128 to 127. There are a number of alternate instruction sequences for the ADDI operation. First, if the immediate is 0, the ADDI will be turned into a MOV.N instruction (or the equivalent OR instruction if the code density option is not available). If the ADDI immediate is outside of the range -128 to 127, but inside the range -32896 to 32639, an ADDMI instruction or ADDMI/ADDI sequence will be used. Finally, if the immediate is outside of this range and a free register is available, an L32R/ADD sequence will be used with a literal allocated from the literal pool.

For example:

    addi    a5, a6, 0
    addi    a5, a6, 512

    addi    a5, a6, 513
    addi    a5, a6, 50000

is assembled into the following:

    .literal .L1, 50000
    mov.n   a5, a6

    addmi   a5, a6, 0x200
    addmi   a5, a6, 0x200
    addi    a5, a5, 1

    l32r    a5, .L1
    add     a5, a6, a5