Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

cmd/compile: use proved bounds to remove signed division fix-ups

Browse source 
prove is able to find 94 occurrences in std cmd where a divisor
can't have the value -1. The change removes
the extraneous fix-up code for these cases.

Fixes #25239

Change-Id: Ic184de971f47cc57c702eb72805b8e291c14035d
Reviewed-on: https://go-review.googlesource.com/c/130215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
ChrisALiles 2018-08-06 19:50:38 +10:00 • committed by Brad Fitzpatrick
parent 47cc59f31f
commit 13d5cd7847
14 changed files with 299 additions and 98 deletions
Download patch file Download diff file Expand all files Collapse all files

23
src/cmd/compile/internal/ssa/prove.go
View file

@ -1076,6 +1076,13 @@ func addLocalInductiveFacts(ft *factsTable, b *Block) {
}
var ctzNonZeroOp = map[Op]Op{OpCtz8: OpCtz8NonZero, OpCtz16: OpCtz16NonZero, OpCtz32: OpCtz32NonZero, OpCtz64: OpCtz64NonZero}
var mostNegativeDividend = map[Op]int64{
OpDiv16: -1 << 15,
OpMod16: -1 << 15,
OpDiv32: -1 << 31,
OpMod32: -1 << 31,
OpDiv64: -1 << 63,
OpMod64: -1 << 63}
// simplifyBlock simplifies some constant values in b and evaluates
// branches to non-uniquely dominated successors of b.
@ -1147,6 +1154,22 @@ func simplifyBlock(sdom SparseTree, ft *factsTable, b *Block) {
b.Func.Warnl(v.Pos, "Proved %v bounded", v.Op)
}
}
case OpDiv16, OpDiv32, OpDiv64, OpMod16, OpMod32, OpMod64:
// On amd64 and 386 fix-up code can be avoided if we know
// the divisor is not -1 or the dividend > MinIntNN.
divr := v.Args[1]
divrLim, divrLimok := ft.limits[divr.ID]
divd := v.Args[0]
divdLim, divdLimok := ft.limits[divd.ID]
if (divrLimok && (divrLim.max < -1 || divrLim.min > -1)) ||
(divdLimok && divdLim.min > mostNegativeDividend[v.Op]) {
v.AuxInt = 1 // see NeedsFixUp in genericOps - v.AuxInt = 0 means we have not proved
// that the divisor is not -1 and the dividend is not the most negative,
// so we need to add fix-up code.
if b.Func.pass.debug > 0 {
b.Func.Warnl(v.Pos, "Proved %v does not need fix-up", v.Op)
}
}
}
}