diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 33 |
1 files changed, 28 insertions, 5 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index 12c2580c95..a8e43d0114 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -1189,15 +1189,38 @@ func simplifyBlock(sdom SparseTree, ft *factsTable, b *Block) { } v.Op = ctzNonZeroOp[v.Op] } - + case OpRsh8x8, OpRsh8x16, OpRsh8x32, OpRsh8x64, + OpRsh16x8, OpRsh16x16, OpRsh16x32, OpRsh16x64, + OpRsh32x8, OpRsh32x16, OpRsh32x32, OpRsh32x64, + OpRsh64x8, OpRsh64x16, OpRsh64x32, OpRsh64x64: + // Check whether, for a >> b, we know that a is non-negative + // and b is all of a's bits except the MSB. If so, a is shifted to zero. + bits := 8 * v.Type.Size() + if v.Args[1].isGenericIntConst() && v.Args[1].AuxInt >= bits-1 && ft.isNonNegative(v.Args[0]) { + if b.Func.pass.debug > 0 { + b.Func.Warnl(v.Pos, "Proved %v shifts to zero", v.Op) + } + switch bits { + case 64: + v.reset(OpConst64) + case 32: + v.reset(OpConst32) + case 16: + v.reset(OpConst16) + case 8: + v.reset(OpConst8) + default: + panic("unexpected integer size") + } + v.AuxInt = 0 + continue // Be sure not to fallthrough - this is no longer OpRsh. + } + // If the Rsh hasn't been replaced with 0, still check if it is bounded. + fallthrough case OpLsh8x8, OpLsh8x16, OpLsh8x32, OpLsh8x64, OpLsh16x8, OpLsh16x16, OpLsh16x32, OpLsh16x64, OpLsh32x8, OpLsh32x16, OpLsh32x32, OpLsh32x64, OpLsh64x8, OpLsh64x16, OpLsh64x32, OpLsh64x64, - OpRsh8x8, OpRsh8x16, OpRsh8x32, OpRsh8x64, - OpRsh16x8, OpRsh16x16, OpRsh16x32, OpRsh16x64, - OpRsh32x8, OpRsh32x16, OpRsh32x32, OpRsh32x64, - OpRsh64x8, OpRsh64x16, OpRsh64x32, OpRsh64x64, OpRsh8Ux8, OpRsh8Ux16, OpRsh8Ux32, OpRsh8Ux64, OpRsh16Ux8, OpRsh16Ux16, OpRsh16Ux32, OpRsh16Ux64, OpRsh32Ux8, OpRsh32Ux16, OpRsh32Ux32, OpRsh32Ux64, |