diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 47 |
1 files changed, 46 insertions, 1 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index 9dca4a439b..eca04e0bf0 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -859,10 +859,55 @@ func prove(f *Func) { case OpOr64, OpOr32, OpOr16, OpOr8: ft.update(b, v, v.Args[1], unsigned, gt|eq) ft.update(b, v, v.Args[0], unsigned, gt|eq) + case OpPhi: + // Determine the min and max value of OpPhi composed entirely of integer constants. + // + // For example, for an OpPhi: + // + // v1 = OpConst64 [13] + // v2 = OpConst64 [7] + // v3 = OpConst64 [42] + // + // v4 = OpPhi(v1, v2, v3) + // + // We can prove: + // + // v4 >= 7 && v4 <= 42 + // + // TODO(jake-ciolek): Handle nested constant OpPhi's + sameConstOp := true + min := 0 + max := 0 + + if !v.Args[min].isGenericIntConst() { + break + } + + for k := range v.Args { + if v.Args[k].Op != v.Args[min].Op { + sameConstOp = false + break + } + if v.Args[k].AuxInt < v.Args[min].AuxInt { + min = k + } + if v.Args[k].AuxInt > v.Args[max].AuxInt { + max = k + } + } + + if sameConstOp { + ft.update(b, v, v.Args[min], signed, gt|eq) + ft.update(b, v, v.Args[max], signed, lt|eq) + } + // One might be tempted to create a v >= ft.zero relation for + // all OpPhi's composed of only provably-positive values + // but that bloats up the facts table for a very neglible gain. + // In Go itself, very few functions get improved (< 5) at a cost of 5-7% total increase + // of compile time. } } } - // Find induction variables. Currently, findIndVars // is limited to one induction variable per block. var indVars map[*Block]indVar |