diff options
Diffstat (limited to 'src/cmd/compile')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index cf045629cb..0c0581690f 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -2164,6 +2164,10 @@ func signedAddOverflowsOrUnderflows(a, b int64, t *types.Type) bool { } } +func unsignedSubUnderflows(a, b uint64) bool { + return a < b +} + func addLocalFacts(ft *factsTable, b *Block) { // Propagate constant ranges among values in this block. // We do this before the second loop so that we have the @@ -2226,6 +2230,17 @@ func addLocalFacts(ft *factsTable, b *Block) { } ft.update(b, v, v.Args[0], signed, r) } + case OpSub64, OpSub32, OpSub16, OpSub8: + x := ft.limits[v.Args[0].ID] + y := ft.limits[v.Args[1].ID] + if !unsignedSubUnderflows(x.umin, y.umax) { + r := lt + if !y.nonzero() { + r |= eq + } + ft.update(b, v, v.Args[0], unsigned, r) + } + // FIXME: we could also do signed facts but the overflow checks are much trickier and I don't need it yet. case OpAnd64, OpAnd32, OpAnd16, OpAnd8: ft.update(b, v, v.Args[0], unsigned, lt|eq) ft.update(b, v, v.Args[1], unsigned, lt|eq) |