diff options
Diffstat (limited to 'vendor/github.com/mmcloughlin/avo/pass/cleanup.go')
-rw-r--r-- | vendor/github.com/mmcloughlin/avo/pass/cleanup.go | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/vendor/github.com/mmcloughlin/avo/pass/cleanup.go b/vendor/github.com/mmcloughlin/avo/pass/cleanup.go new file mode 100644 index 0000000..d91250f --- /dev/null +++ b/vendor/github.com/mmcloughlin/avo/pass/cleanup.go @@ -0,0 +1,123 @@ +package pass + +import ( + "github.com/mmcloughlin/avo/ir" + "github.com/mmcloughlin/avo/operand" +) + +// PruneJumpToFollowingLabel removes jump instructions that target an +// immediately following label. +func PruneJumpToFollowingLabel(fn *ir.Function) error { + for i := 0; i+1 < len(fn.Nodes); i++ { + node := fn.Nodes[i] + next := fn.Nodes[i+1] + + // This node is an unconditional jump. + inst, ok := node.(*ir.Instruction) + if !ok || !inst.IsBranch || inst.IsConditional { + continue + } + + target := inst.TargetLabel() + if target == nil { + continue + } + + // And the jump target is the immediately following node. + lbl, ok := next.(ir.Label) + if !ok || lbl != *target { + continue + } + + // Then the jump is unnecessary and can be removed. + fn.Nodes = deletenode(fn.Nodes, i) + i-- + } + + return nil +} + +// PruneDanglingLabels removes labels that are not referenced by any branches. +func PruneDanglingLabels(fn *ir.Function) error { + // Count label references. + count := map[ir.Label]int{} + for _, n := range fn.Nodes { + i, ok := n.(*ir.Instruction) + if !ok || !i.IsBranch { + continue + } + + target := i.TargetLabel() + if target == nil { + continue + } + + count[*target]++ + } + + // Look for labels with no references. + for i := 0; i < len(fn.Nodes); i++ { + node := fn.Nodes[i] + lbl, ok := node.(ir.Label) + if !ok { + continue + } + + if count[lbl] == 0 { + fn.Nodes = deletenode(fn.Nodes, i) + i-- + } + } + + return nil +} + +// PruneSelfMoves removes move instructions from one register to itself. +func PruneSelfMoves(fn *ir.Function) error { + return removeinstructions(fn, func(i *ir.Instruction) bool { + switch i.Opcode { + case "MOVB", "MOVW", "MOVL", "MOVQ": + default: + return false + } + + return operand.IsRegister(i.Operands[0]) && operand.IsRegister(i.Operands[1]) && i.Operands[0] == i.Operands[1] + }) +} + +// removeinstructions deletes instructions from the given function which match predicate. +func removeinstructions(fn *ir.Function, predicate func(*ir.Instruction) bool) error { + // Removal of instructions has the potential to invalidate CFG structures. + // Clear them to prevent accidental use of stale structures after this pass. + invalidatecfg(fn) + + for i := 0; i < len(fn.Nodes); i++ { + n := fn.Nodes[i] + + inst, ok := n.(*ir.Instruction) + if !ok || !predicate(inst) { + continue + } + + fn.Nodes = deletenode(fn.Nodes, i) + } + + return nil +} + +// deletenode deletes node i from nodes and returns the resulting slice. +func deletenode(nodes []ir.Node, i int) []ir.Node { + n := len(nodes) + copy(nodes[i:], nodes[i+1:]) + nodes[n-1] = nil + return nodes[:n-1] +} + +// invalidatecfg clears CFG structures. +func invalidatecfg(fn *ir.Function) { + fn.LabelTarget = nil + for _, i := range fn.Instructions() { + i.Pred = nil + i.Succ = nil + } +} |