6.45.3.1. Simple Constraints
6.45.3.1 Simple Constraints
The simplest kind of constraint is a string full of letters, each of which describes one kind of operand that is permitted. Here are the letters that are allowed:
- whitespace
-
Whitespace characters are ignored and can be inserted at any position except the first. This enables each alternative for different operands to be visually aligned in the machine description even if they have different number of constraints and modifiers.
- ‘m’
-
A memory operand is allowed, with any kind of address that the machine supports in general. Note that the letter used for the general memory constraint can be re-defined by a back end using the
TARGET_MEM_CONSTRAINTmacro. - ‘o’
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