1117238 - Use the BMI instruction sets on x86

Status: NEW

(Core :: JavaScript Engine: JIT, enhancement, P5)

Description

[Jan de Mooij [:jandem]]

On x86, shift instructions require the RHS to be in ECX if it's not a constant. This is pretty annoying for the register allocators.

The BMI2 instruction set (Haswell+) adds new (ternary) shift instructions (SARX/SHLX/SHRX) that don't have this restriction. It could also avoid some other move instructions because the output can be different from the inputs.

The BZHI instruction could be used to unbox Values on x64:

    movb	  $47, output
    bzhiq output, input, output

This might be shorter than:

    movq JSVAL_PAYLOAD_MASK, output
    andq input, output