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| author | Cuong Manh Le <cuong.manhle.vn@gmail.com> | 2020-04-01 05:27:49 +0700 |
|---|---|---|
| committer | Matthew Dempsky <mdempsky@google.com> | 2020-03-31 23:39:12 +0000 |
| commit | 6edd7971bb3e83356544b2cd6e7a93fdabff1246 (patch) | |
| tree | 97f17bb5205184633e5dc765db35f5de9090d50d | |
| parent | 82253ddc7a6b85240fd74cc5138f685ca931f355 (diff) | |
| download | go-6edd7971bb3e83356544b2cd6e7a93fdabff1246.tar.gz go-6edd7971bb3e83356544b2cd6e7a93fdabff1246.zip | |
cmd/compile: optimize len check when make slice
In CL 226278, we did:
if len < 0 { panicmakeslicelen }
if len > cap { panicmakeslicecap }
But due to the fact that cap is constrained to [0,2^31), so it is safe
to do:
if uint64(len) > cap {
if len < 0 { panicmakeslicelen() }
panicmakeslicecap()
}
save us a comparison in common case when len is within range.
Passes toolstash-check.
Change-Id: I0ebd52914ccde4cbb45f16c9e020b0c8f42e0663
Reviewed-on: https://go-review.googlesource.com/c/go/+/226737
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
| -rw-r--r-- | src/cmd/compile/internal/gc/walk.go | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go index dfc9d9aa22..14d088c7fd 100644 --- a/src/cmd/compile/internal/gc/walk.go +++ b/src/cmd/compile/internal/gc/walk.go @@ -1338,15 +1338,16 @@ opswitch: Fatalf("walkexpr: invalid index %v", r) } - // if len < 0 { panicmakeslicelen } - nif := nod(OIF, nod(OLT, l, nodintconst(0)), nil) - nif.Nbody.Set1(mkcall("panicmakeslicelen", nil, init)) - nif = typecheck(nif, ctxStmt) - init.Append(nif) - - // if len > cap { panicmakeslicecap } - nif = nod(OIF, nod(OGT, conv(l, types.Types[TUINT64]), nodintconst(i)), nil) - nif.Nbody.Set1(mkcall("panicmakeslicecap", nil, init)) + // cap is constrained to [0,2^31), so it's safe to do: + // + // if uint64(len) > cap { + // if len < 0 { panicmakeslicelen() } + // panicmakeslicecap() + // } + nif := nod(OIF, nod(OGT, conv(l, types.Types[TUINT64]), nodintconst(i)), nil) + niflen := nod(OIF, nod(OLT, l, nodintconst(0)), nil) + niflen.Nbody.Set1(mkcall("panicmakeslicelen", nil, init)) + nif.Nbody.Append(niflen, mkcall("panicmakeslicecap", nil, init)) nif = typecheck(nif, ctxStmt) init.Append(nif) |