Instruction

class Instruction (abstract, logical)

An instruction within a control flow block.

Evaluation of an instruction happens in these separate steps:

1. fetching of input operands (SLoc currently not stored in IR)

2. computation of the address for the left (output) operand (SLoc via Left_Physical)

3. evaluation of the instruction = computation of the instruction’s value (SLoc via Physical)

4. storage of the value in the write operand (SLoc via Physical_For_Assignment)

Some instructions are exceptions to this evaluation schema, e.g.:

• Discard_Instruction does not fetch the input operands

• Call_Instruction uses “alias semantics” for input operands and the output operand; and thus does not have step 1 or step 4 as such.

See those instructions for more details.

Direct parents:

• inherits Execution_Node

Ancestor classes and implemented interfaces:

Execution_Node, Logical_IR_Root

Direct child classes:

• subclass Exit_Scope_Instruction

• subclass Copy_Assignment_Instruction

• subclass Error_Instruction

• subclass Assembler_Instruction

• subclass Unary_Instruction

• subclass Binary_Instruction

• subclass Vector_Select_Instruction

• subclass VLA_Allocate_Instruction

• subclass Platform_Select_Instruction

• subclass Literal_Instruction

• subclass Call_Instruction

• subclass Managed_New_Buffer_Instruction

• subclass Managed_Type_Of_Instruction

Field	Kind	Type	Description
Left	syntactic	class Operand	Where the result will be stored. This is always a write operand. (can be NULL, e.g., for calls to void funcs or assertion instructions. Check cafe’s can_omit_lhs() for the full list of instructions that can have Left equal to NoNode.)
Left_Physical	semantic to physical	class Physical_IR_Root	This edge instead points to the expression that represents the left operand, i.e., the expression that computed the glvalue where the result of the instruction will be stored. For example, in v = 42; (a LIR Integer_Literal_Instruction): The Physical edge points to the PIR Integer_Literal. The Left_Physical edge points to the Unqualified_Direct_Object_Selection for the variable v. And the Physical_For_Assignment edge points to the Assignment expression.
Its_Type	semantic	class Type	Result type of the instruction, needed especially to distinguish assignments of complete structs from assignments of their first fields. Also needed to determine multiplication factor for pointer additions. For Cast_Instructions, this is the type casted to
Physical_For_Assignment	semantic to physical	class Physical_IR_Root	Returns a PIR node for the assignment of the value that was computed by this instruction. For example, in v = 42; (a LIR Integer_Literal_Instruction): The Physical edge points to the PIR Integer_Literal. The Left_Physical edge points to the Unqualified_Direct_Object_Selection for the variable v. And the Physical_For_Assignment edge points to the Assignment expression.
Parent (from Logical_IR_Root)	semantic	class CFG_Standard_Block
Physical (from Logical_IR_Root)	semantic to physical	class Physical_IR_Root