private void OptimizeGeneratedCode()
{
var Instructions = code.Instructions;
var StackMap = code.StackMap;
int n = Instructions.Count;
//
// nop optimization:
//
// remove any nop instructions that are not a branch target,
// and only if there are no exception tables. note that
// removing nops that are a branch target, or nops in a method
// with exception tables, would require updating the stack map,
// branch instructions and exception tables.
//
var nops = new List <int>();
bool discardNops =
(code.Exceptions == null || code.Exceptions.Count == 0);
// constants optimization:
//
// find occurrences of iconst_0 or iconst_1 followed by i2l
// (which must not be a branch target), and convert to lconst_xx
//
for (int i = 0; i < n; i++)
{
byte op = Instructions[i].Opcode;
if (op == 0x00 /* nop */)
{
// collect this nop only if it is not a branch target
if (!StackMap.HasBranchFrame(Instructions[i].Label))
{
nops.Add(i);
}
}
else if (JavaCode.IsBranchOpcode(op)) // jump inst
{
if (Instructions[i].Data is int)
{
// if jump instruction has an explicit byte offset,
// we can't do nop elimination; see FillJumpTargets
// in JavaBinary.JavaCodeWriter
discardNops = false;
}
}
else if (op == 0x85 /* i2l */ && i > 0)
{
var prevInst = Instructions[i - 1];
if (prevInst.Opcode == 0x12 && /* ldc */
prevInst.Data is int intValue &&
(intValue == 0 || intValue == 1) &&
(!StackMap.HasBranchFrame(
Instructions[i].Label)))
{
// convert ldc of 0 or 1 into lconst_0 or lconst_1
prevInst.Opcode = (byte)(intValue + 0x09);
// convert current instruction to nop,
// and mark to discard it if discarding nops
Instructions[i].Opcode = 0x00; // nop
nops.Add(i);
}
}
}
if (discardNops)
{
for (int i = nops.Count; i-- > 0;)
{
Instructions.RemoveAt(nops[i]);
}
}
}