path: root/llvm/docs/GlobalISel/GenericOpcode.rst

.. _gmir-opcodes:

Generic Opcodes
===============

.. contents::
   :local:

.. note::

  This documentation does not yet fully account for vectors. Many of the
  scalar/integer/floating-point operations can also take vectors.

Constants
---------

G_IMPLICIT_DEF
^^^^^^^^^^^^^^

An undefined value.

.. code-block:: none

  %0:_(s32) = G_IMPLICIT_DEF

G_CONSTANT
^^^^^^^^^^

An integer constant.

.. code-block:: none

  %0:_(s32) = G_CONSTANT i32 1

G_FCONSTANT
^^^^^^^^^^^

A floating point constant.

.. code-block:: none

  %0:_(s32) = G_FCONSTANT float 1.0

G_FRAME_INDEX
^^^^^^^^^^^^^

The address of an object in the stack frame.

.. code-block:: none

  %1:_(p0) = G_FRAME_INDEX %stack.0.ptr0

G_GLOBAL_VALUE
^^^^^^^^^^^^^^

The address of a global value.

.. code-block:: none

  %0(p0) = G_GLOBAL_VALUE @var_local

G_BLOCK_ADDR
^^^^^^^^^^^^

The address of a basic block.

.. code-block:: none

  %0:_(p0) = G_BLOCK_ADDR blockaddress(@test_blockaddress, %ir-block.block)

Integer Extension and Truncation
--------------------------------

G_ANYEXT
^^^^^^^^

Extend the underlying scalar type of an operation, leaving the high bits
unspecified.

.. code-block:: none

  %1:_(s32) = G_ANYEXT %0:_(s16)

G_SEXT
^^^^^^

Sign extend the underlying scalar type of an operation, copying the sign bit
into the newly-created space.

.. code-block:: none

  %1:_(s32) = G_SEXT %0:_(s16)

G_SEXT_INREG
^^^^^^^^^^^^

Sign extend the value from an arbitrary bit position, copying the sign bit
into all bits above it. This is equivalent to a shl + ashr pair with an
appropriate shift amount. $sz is an immediate (MachineOperand::isImm()
returns true) to allow targets to have some bitwidths legal and others
lowered. This opcode is particularly useful if the target has sign-extension
instructions that are cheaper than the constituent shifts as the optimizer is
able to make decisions on whether it's better to hang on to the G_SEXT_INREG
or to lower it and optimize the individual shifts.

.. code-block:: none

  %1:_(s32) = G_SEXT_INREG %0:_(s32), 16

G_ZEXT
^^^^^^

Zero extend the underlying scalar type of an operation, putting zero bits
into the newly-created space.

.. code-block:: none

  %1:_(s32) = G_ZEXT %0:_(s16)

G_TRUNC
^^^^^^^

Truncate the underlying scalar type of an operation. This is equivalent to
G_EXTRACT for scalar types, but acts elementwise on vectors.

.. code-block:: none

  %1:_(s16) = G_TRUNC %0:_(s32)

Type Conversions
----------------

G_INTTOPTR
^^^^^^^^^^

Convert an integer to a pointer.

.. code-block:: none

  %1:_(p0) = G_INTTOPTR %0:_(s32)

G_PTRTOINT
^^^^^^^^^^

Convert a pointer to an integer.

.. code-block:: none

  %1:_(s32) = G_PTRTOINT %0:_(p0)

G_BITCAST
^^^^^^^^^

Reinterpret a value as a new type. This is usually done without changing any
bits but this is not always the case due a sublety in the definition of the
:ref:`LLVM-IR Bitcast Instruction <i_bitcast>`.

.. code-block:: none

  %1:_(s64) = G_BITCAST %0:_(<2 x s32>)

G_ADDRSPACE_CAST
^^^^^^^^^^^^^^^^

Convert a pointer to an address space to a pointer to another address space.

.. code-block:: none

  %1:_(p1) = G_ADDRSPACE_CAST %0:_(p0)

.. caution::

  :ref:`i_addrspacecast` doesn't mention what happens if the cast is simply
  invalid (i.e. if the address spaces are disjoint).

Scalar Operations
-----------------

G_EXTRACT
^^^^^^^^^

Extract a register of the specified size, starting from the block given by
index. This will almost certainly be mapped to sub-register COPYs after
register banks have been selected.

G_INSERT
^^^^^^^^

Insert a smaller register into a larger one at the specified bit-index.

G_MERGE_VALUES
^^^^^^^^^^^^^^

Concatenate multiple registers of the same size into a wider register.
The input operands are always ordered from lowest bits to highest:

.. code-block:: none

  %0:(s32) = G_MERGE_VALUES %bits_0_7:(s8), %bits_8_15:(s8),
                            %bits_16_23:(s8), %bits_24_31:(s8)

G_UNMERGE_VALUES
^^^^^^^^^^^^^^^^

Extract multiple registers of the specified size, starting from blocks given by
indexes. This will almost certainly be mapped to sub-register COPYs after
register banks have been selected.
The output operands are always ordered from lowest bits to highest:

.. code-block:: none

  %bits_0_7:(s8), %bits_8_15:(s8),
      %bits_16_23:(s8), %bits_24_31:(s8) = G_UNMERGE_VALUES %0:(s32)

G_BSWAP
^^^^^^^

Reverse the order of the bytes in a scalar.

.. code-block:: none

  %1:_(s32) = G_BSWAP %0:_(s32)

G_BITREVERSE
^^^^^^^^^^^^

Reverse the order of the bits in a scalar.

.. code-block:: none

  %1:_(s32) = G_BITREVERSE %0:_(s32)

Integer Operations
-------------------

G_ADD, G_SUB, G_MUL, G_AND, G_OR, G_XOR, G_SDIV, G_UDIV, G_SREM, G_UREM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

These each perform their respective integer arithmetic on a scalar.

.. code-block:: none

  %2:_(s32) = G_ADD %0:_(s32), %1:_(s32)

G_SHL, G_LSHR, G_ASHR
^^^^^^^^^^^^^^^^^^^^^

Shift the bits of a scalar left or right inserting zeros (sign-bit for G_ASHR).

G_ICMP
^^^^^^

Perform integer comparison producing non-zero (true) or zero (false). It's
target specific whether a true value is 1, ~0U, or some other non-zero value.

G_SELECT
^^^^^^^^

Select between two values depending on a zero/non-zero value.

.. code-block:: none

  %5:_(s32) = G_SELECT %4(s1), %6, %2

G_PTR_ADD
^^^^^^^^^

Add a scalar offset in addressible units to a pointer. Addressible units are
typically bytes but this may vary between targets.

.. code-block:: none

  %1:_(p0) = G_PTR_ADD %0:_(p0), %1:_(s32)

.. caution::

  There are currently no in-tree targets that use this with addressable units
  not equal to 8 bit.

G_PTR_MASK
^^^^^^^^^^

Zero the least significant N bits of a pointer.

.. code-block:: none

  %1:_(p0) = G_PTR_MASK %0, 3

G_SMIN, G_SMAX, G_UMIN, G_UMAX
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Take the minimum/maximum of two values.

.. code-block:: none

  %5:_(s32) = G_SMIN %6, %2

G_UADDO, G_SADDO, G_USUBO, G_SSUBO, G_SMULO, G_UMULO
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Perform the requested arithmetic and produce a carry output in addition to the
normal result.

.. code-block:: none

  %3:_(s32), %4:_(s1) = G_UADDO %0, %1

G_UADDE, G_SADDE, G_USUBE, G_SSUBE
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Perform the requested arithmetic and consume a carry input in addition to the
normal input. Also produce a carry output in addition to the normal result.

.. code-block:: none

  %4:_(s32), %5:_(s1) = G_UADDE %0, %1, %3:_(s1)

G_UMULH, G_SMULH
^^^^^^^^^^^^^^^^

Multiply two numbers at twice the incoming bit width (signed) and return
the high half of the result.

.. code-block:: none

  %3:_(s32) = G_UMULH %0, %1

G_CTLZ, G_CTTZ, G_CTPOP
^^^^^^^^^^^^^^^^^^^^^^^

Count leading zeros, trailing zeros, or number of set bits.

.. code-block:: none

  %2:_(s33) = G_CTLZ_ZERO_UNDEF %1
  %2:_(s33) = G_CTTZ_ZERO_UNDEF %1
  %2:_(s33) = G_CTPOP %1

G_CTLZ_ZERO_UNDEF, G_CTTZ_ZERO_UNDEF
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Count leading zeros or trailing zeros. If the value is zero then the result is
undefined.

.. code-block:: none

  %2:_(s33) = G_CTLZ_ZERO_UNDEF %1
  %2:_(s33) = G_CTTZ_ZERO_UNDEF %1

Floating Point Operations
-------------------------

G_FCMP
^^^^^^

Perform floating point comparison producing non-zero (true) or zero
(false). It's target specific whether a true value is 1, ~0U, or some other
non-zero value.

G_FNEG
^^^^^^

Floating point negation.

G_FPEXT
^^^^^^^

Convert a floating point value to a larger type.

G_FPTRUNC
^^^^^^^^^

Convert a floating point value to a narrower type.

G_FPTOSI, G_FPTOUI, G_SITOFP, G_UITOFP
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Convert between integer and floating point.

G_FABS
^^^^^^

Take the absolute value of a floating point value.

G_FCOPYSIGN
^^^^^^^^^^^

Copy the value of the first operand, replacing the sign bit with that of the
second operand.

G_FCANONICALIZE
^^^^^^^^^^^^^^^

See :ref:`i_intr_llvm_canonicalize`.

G_FMINNUM
^^^^^^^^^

Perform floating-point minimum on two values.

In the case where a single input is a NaN (either signaling or quiet),
the non-NaN input is returned.

The return value of (FMINNUM 0.0, -0.0) could be either 0.0 or -0.0.

G_FMAXNUM
^^^^^^^^^

Perform floating-point maximum on two values.

In the case where a single input is a NaN (either signaling or quiet),
the non-NaN input is returned.

The return value of (FMAXNUM 0.0, -0.0) could be either 0.0 or -0.0.

G_FMINNUM_IEEE
^^^^^^^^^^^^^^

Perform floating-point minimum on two values, following the IEEE-754 2008
definition. This differs from FMINNUM in the handling of signaling NaNs. If one
input is a signaling NaN, returns a quiet NaN.

G_FMAXNUM_IEEE
^^^^^^^^^^^^^^

Perform floating-point maximum on two values, following the IEEE-754 2008
definition. This differs from FMAXNUM in the handling of signaling NaNs. If one
input is a signaling NaN, returns a quiet NaN.

G_FMINIMUM
^^^^^^^^^^

NaN-propagating minimum that also treat -0.0 as less than 0.0. While
FMINNUM_IEEE follow IEEE 754-2008 semantics, FMINIMUM follows IEEE 754-2018
draft semantics.

G_FMAXIMUM
^^^^^^^^^^

NaN-propagating maximum that also treat -0.0 as less than 0.0. While
FMAXNUM_IEEE follow IEEE 754-2008 semantics, FMAXIMUM follows IEEE 754-2018
draft semantics.

G_FADD, G_FSUB, G_FMUL, G_FDIV, G_FREM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Perform the specified floating point arithmetic.

G_FMA
^^^^^

Perform a fused multiply add (i.e. without the intermediate rounding step).

G_FMAD
^^^^^^

Perform a non-fused multiply add (i.e. with the intermediate rounding step).

G_FPOW
^^^^^^

Raise the first operand to the power of the second.

G_FEXP, G_FEXP2
^^^^^^^^^^^^^^^

Calculate the base-e or base-2 exponential of a value

G_FLOG, G_FLOG2, G_FLOG10
^^^^^^^^^^^^^^^^^^^^^^^^^

Calculate the base-e, base-2, or base-10 respectively.

G_FCEIL, G_FCOS, G_FSIN, G_FSQRT, G_FFLOOR, G_FRINT, G_FNEARBYINT
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

These correspond to the standard C functions of the same name.

G_INTRINSIC_TRUNC
^^^^^^^^^^^^^^^^^

Returns the operand rounded to the nearest integer not larger in magnitude than the operand.

G_INTRINSIC_ROUND
^^^^^^^^^^^^^^^^^

Returns the operand rounded to the nearest integer.

Vector Specific Operations
--------------------------

G_CONCAT_VECTORS
^^^^^^^^^^^^^^^^

Concatenate two vectors to form a longer vector.

G_BUILD_VECTOR, G_BUILD_VECTOR_TRUNC
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Create a vector from multiple scalar registers. No implicit
conversion is performed (i.e. the result element type must be the
same as all source operands)

The _TRUNC version truncates the larger operand types to fit the
destination vector elt type.

G_INSERT_VECTOR_ELT
^^^^^^^^^^^^^^^^^^^

Insert an element into a vector

G_EXTRACT_VECTOR_ELT
^^^^^^^^^^^^^^^^^^^^

Extract an element from a vector

G_SHUFFLE_VECTOR
^^^^^^^^^^^^^^^^

Concatenate two vectors and shuffle the elements according to the mask operand.
The mask operand should be an IR Constant which exactly matches the
corresponding mask for the IR shufflevector instruction.

Memory Operations
-----------------

G_LOAD, G_SEXTLOAD, G_ZEXTLOAD
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Generic load. Expects a MachineMemOperand in addition to explicit
operands. If the result size is larger than the memory size, the
high bits are undefined, sign-extended, or zero-extended respectively.

Only G_LOAD is valid if the result is a vector type. If the result is larger
than the memory size, the high elements are undefined (i.e. this is not a
per-element, vector anyextload)

G_INDEXED_LOAD
^^^^^^^^^^^^^^

Generic indexed load. Combines a GEP with a load. $newaddr is set to $base + $offset.
If $am is 0 (post-indexed), then the value is loaded from $base; if $am is 1 (pre-indexed)
then the value is loaded from $newaddr.

G_INDEXED_SEXTLOAD
^^^^^^^^^^^^^^^^^^

Same as G_INDEXED_LOAD except that the load performed is sign-extending, as with G_SEXTLOAD.

G_INDEXED_ZEXTLOAD
^^^^^^^^^^^^^^^^^^

Same as G_INDEXED_LOAD except that the load performed is zero-extending, as with G_ZEXTLOAD.

G_STORE
^^^^^^^

Generic store. Expects a MachineMemOperand in addition to explicit operands.

G_INDEXED_STORE
^^^^^^^^^^^^^^^

Combines a store with a GEP. See description of G_INDEXED_LOAD for indexing behaviour.

G_ATOMIC_CMPXCHG_WITH_SUCCESS
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Generic atomic cmpxchg with internal success check. Expects a
MachineMemOperand in addition to explicit operands.

G_ATOMIC_CMPXCHG
^^^^^^^^^^^^^^^^

Generic atomic cmpxchg. Expects a MachineMemOperand in addition to explicit
operands.

G_ATOMICRMW_XCHG, G_ATOMICRMW_ADD, G_ATOMICRMW_SUB, G_ATOMICRMW_AND, G_ATOMICRMW_NAND, G_ATOMICRMW_OR, G_ATOMICRMW_XOR, G_ATOMICRMW_MAX, G_ATOMICRMW_MIN, G_ATOMICRMW_UMAX, G_ATOMICRMW_UMIN, G_ATOMICRMW_FADD, G_ATOMICRMW_FSUB
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Generic atomicrmw. Expects a MachineMemOperand in addition to explicit
operands.

G_FENCE
^^^^^^^

.. caution::

  I couldn't find any documentation on this at the time of writing.

Control Flow
------------

G_PHI
^^^^^

Implement the φ node in the SSA graph representing the function.

.. code-block:: none

  %1(s8) = G_PHI %7(s8), %bb.0, %3(s8), %bb.1

G_BR
^^^^

Unconditional branch

G_BRCOND
^^^^^^^^

Conditional branch

G_BRINDIRECT
^^^^^^^^^^^^

Indirect branch

G_BRJT
^^^^^^

Indirect branch to jump table entry

G_JUMP_TABLE
^^^^^^^^^^^^

.. caution::

  I found no documentation for this instruction at the time of writing.

G_INTRINSIC, G_INTRINSIC_W_SIDE_EFFECTS
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Call an intrinsic

The _W_SIDE_EFFECTS version is considered to have unknown side-effects and
as such cannot be reordered acrosss other side-effecting instructions.

.. note::

  Unlike SelectionDAG, there is no _VOID variant. Both of these are permitted
  to have zero, one, or multiple results.

Variadic Arguments
------------------

G_VASTART
^^^^^^^^^

.. caution::

  I found no documentation for this instruction at the time of writing.

G_VAARG
^^^^^^^

.. caution::

  I found no documentation for this instruction at the time of writing.

Other Operations
----------------

G_DYN_STACKALLOC
^^^^^^^^^^^^^^^^

Dynamically realign the stack pointer to the specified alignment

.. code-block:: none

  %8:_(p0) = G_DYN_STACKALLOC %7(s64), 32

.. caution::

  What does it mean for the immediate to be 0? It happens in the tests