• Cherry Zhang's avatar
    [dev.ssa] cmd/internal/obj/arm64: fix encoding constant into some instructions · 748aa844
    Cherry Zhang authored
    When a constant can be encoded in a logical instruction (BITCON), do
    it this way instead of using the constant pool. The BITCON testing
    code runs faster than table lookup (using map):
    
    (on AMD64 machine, with pseudo random input)
    BenchmarkIsBitcon-4   	300000000	         4.04 ns/op
    BenchmarkTable-4      	50000000	        27.3 ns/op
    
    The equivalent C code of BITCON testing is formally verified with
    model checker CBMC against linear search of the lookup table.
    
    Also handle cases when a constant can be encoded in a MOV instruction.
    In this case, materializa the constant into REGTMP without using the
    constant pool.
    
    When constants need to be added to the constant pool, make sure to
    check whether it fits in 32-bit. If not, store 64-bit.
    
    Both legacy and SSA compiler backends are happy with this.
    
    Fixes #16226.
    
    Change-Id: I883e3069dee093a1cdc40853c42221a198a152b0
    Reviewed-on: https://go-review.googlesource.com/26631
    Run-TryBot: Cherry Zhang <cherryyz@google.com>
    Reviewed-by: default avatarDavid Chase <drchase@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    748aa844
asm7.go 96.6 KB