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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
IFCALL = 0x4f
## Format
| | | | | |
| --- | --- | --- | --- | --- |
| 0x4f(IFCALL) | Exec_size | Pred | Func_addr | Arg_size | Return_size |
## Semantics
Calls the function located at <func_addr>
## Description
Calls the function located at <func_addr> based on the predicate value.
- **Exec_size(ub):** Execution size
- Bit[2..0]: size of the region for source and destination operands
- 0b000: 1 element (scalar)
- 0b001: 2 elements
- 0b010: 4 elements
- 0b011: 8 elements
- 0b100: 16 elements
- 0b101: 32 elements
- Bit[7..4]: execution mask (explicit control over the enabled channels)
- 0b0000: M1
- 0b0001: M2
- 0b0010: M3
- 0b0011: M4
- 0b0100: M5
- 0b0101: M6
- 0b0110: M7
- 0b0111: M8
- 0b1000: M1_NM
- 0b1001: M2_NM
- 0b1010: M3_NM
- 0b1011: M4_NM
- 0b1100: M5_NM
- 0b1101: M6_NM
- 0b1110: M7_NM
- 0b1111: M8_NM
- **Pred(uw):** Predication control
- **Func_addr(scalar):** A scalar value representing the address of the function being called. Must have type UD
- **Arg_size(ub):** Argument size in unit of GRF. Valid values are [0-%arg]
- **Return_size(ub):** Return size in unit of GRF. Valid values are [0-%retval]
#### Properties
## Text
```
[(<P>)] IFCALL (<exec_size>) <func_id> <arg_size> <return_size>
```
## Notes
If <exec_size> is one: Execution jumps to the function if the predicate is true. The call mask will be initialized to all ones at function entry. Scalar calls must be marked with {NoMask}.
If <exec_size> is greater than one: The call is executed if any of the active channels are predicated. At function entry, the call mask will be initialized to the set of active channels that are predicated.
<func_addr> is a 32-bit unsigned integer value that represents the address of a vISA function. The FADDR instruction may be used to obtain the value of a vISA function's address.
The behavior is undefined if <func_addr> is not the address of any of the functions.
If the call is executed, this instruction copies the first <arg_size> GRFs of %arg from the caller to the callee, destroying its contents in the caller during the process. It also copies the value of stack (%sp) and frame pointer (%fp) from the caller to the callee. When the call returns, the first <return_size> GRFs of %retval holds the return values. It is an error if <arg_size> and <return_size> do not match the callee's declared values.
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