binutils Newspaper
JULY 29, 2026
x86 Proposed

x86: Simplify base opcode setting in optimize_encoding().

Simplifies an opcode calculation in the x86 assembler's encoding optimization.

This patch simplifies a specific case within the optimize_encoding function in the x86 assembler configuration. It removes redundant logic for setting the base opcode, making the code slightly cleaner by directly assigning the known value when certain conditions are met, as the W property is evaluated later.

In Details

Refactors the x86 assembler's optimize_encoding function to simplify the determination of the base opcode. It addresses a specific conditional block where the base opcode is set to 0x84 with a potential bitwise OR. The patch removes the bitwise OR, directly setting the base opcode to 0x84, as the 'W' property's evaluation timing makes the OR operation unnecessary.

For Context
opcode
The part of a machine language instruction that specifies the operation to be performed.
optimize_encoding
A function within the assembler that attempts to use more compact instruction encodings where possible.
base opcode
The primary byte that identifies an instruction's operation, often followed by modifiers or operands.
Filed Under: x86assembleroptimizationcode generation