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cmd/compile: intrinsify math/bits.Len on riscv64

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For riscv64/rva22u64 and above, we can intrinsify math/bits.Len using the
CLZ/CLZW machine instructions.

On a StarFive VisionFive 2 with GORISCV64=rva22u64:

                 │   clz.b.1   │               clz.b.2               │
                 │   sec/op    │   sec/op     vs base                │
LeadingZeros-4     28.89n ± 0%   12.08n ± 0%  -58.19% (p=0.000 n=10)
LeadingZeros8-4    18.79n ± 0%   14.76n ± 0%  -21.45% (p=0.000 n=10)
LeadingZeros16-4   25.27n ± 0%   14.76n ± 0%  -41.59% (p=0.000 n=10)
LeadingZeros32-4   25.12n ± 0%   12.08n ± 0%  -51.92% (p=0.000 n=10)
LeadingZeros64-4   25.89n ± 0%   12.08n ± 0%  -53.35% (p=0.000 n=10)
geomean            24.55n        13.09n       -46.70%

Change-Id: I0dda684713dbdf5336af393f5ccbdae861c4f694
Reviewed-on: https://go-review.googlesource.com/c/go/+/652321
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Joel Sing 2025-02-24 00:27:34 +11:00
parent af133d86e4
commit b70244ff7a
8 changed files with 195 additions and 31 deletions
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2
src/cmd/compile/internal/ssa/_gen/RISCV64Ops.go
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@ -229,6 +229,8 @@ func init() {
{name: "AND", argLength: 2, reg: gp21, asm: "AND", commutative: true}, // arg0 & arg1
{name: "ANDN", argLength: 2, reg: gp21, asm: "ANDN"}, // ^arg0 & arg1
{name: "ANDI", argLength: 1, reg: gp11, asm: "ANDI", aux: "Int64"}, // arg0 & auxint
{name: "CLZ", argLength: 1, reg: gp11, asm: "CLZ"}, // count leading zeros
{name: "CLZW", argLength: 1, reg: gp11, asm: "CLZW"}, // count leading zeros of least significant word
{name: "CTZ", argLength: 1, reg: gp11, asm: "CTZ"}, // count trailing zeros
{name: "CTZW", argLength: 1, reg: gp11, asm: "CTZW"}, // count trailing zeros of least significant word
{name: "NOT", argLength: 1, reg: gp11, asm: "NOT"}, // ^arg0