diff options
| author | Austin Clements <austin@google.com> | 2018-01-11 14:23:01 -0500 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2018-03-08 22:25:27 +0000 |
| commit | 941fc129e2f059a5fb9f5ab77f5cb12aedecd145 (patch) | |
| tree | c2664f371770c4508d0e98a27271f27f15a9cce9 /src | |
| parent | 669db2cef55321b0fe354b8bf9212245dc9c6aed (diff) | |
| download | go-941fc129e2f059a5fb9f5ab77f5cb12aedecd145.tar.xz | |
cmd/compile: derive unsigned limits from signed limits in prove
This adds a few simple deductions to the prove pass' fact table to
derive unsigned concrete limits from signed concrete limits where
possible.
This tweak lets the pass prove 70 additional branch conditions in std
and cmd.
This is based on a comment from the recently-deleted factsTable.get:
"// TODO: also use signed data if lim.min >= 0".
Change-Id: Ib4340249e7733070f004a0aa31254adf5df8a392
Reviewed-on: https://go-review.googlesource.com/87479
Reviewed-by: Alexandru Moșoi <alexandru@mosoi.ro>
Reviewed-by: Keith Randall <khr@golang.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index 172d210216..10a16917b6 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -248,6 +248,16 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) { lim.min = c lim.max = c } + if lim.min >= 0 { + // int(x) >= 0 && int(x) >= N ⇒ uint(x) >= N + lim.umin = uint64(lim.min) + } + if lim.max != noLimit.max && old.min >= 0 && lim.max >= 0 { + // 0 <= int(x) <= N ⇒ 0 <= uint(x) <= N + // This is for a max update, so the lower bound + // comes from what we already know (old). + lim.umax = uint64(lim.max) + } case unsigned: var uc uint64 switch w.Op { @@ -281,6 +291,9 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) { lim.umin = uc lim.umax = uc } + // We could use the contrapositives of the + // signed implications to derive signed facts, + // but it turns out not to matter. } ft.limitStack = append(ft.limitStack, limitFact{v.ID, old}) lim = old.intersect(lim) |