public override BlockFlow Emit(
FlowGraphBuilder graph,
ValueTag value)
{
// Create the following blocks:
//
// bitswitch.entry():
// minvalue = const <MinValue>
// switchval.adjusted = switchval - minvalue
// switchval.unsigned = (uintX)switchval.adjusted
// valrange = const <ValueRange>
// switch (switchval.unsigned > valrange)
// 0 -> bitswitch.header()
// default -> <defaultBranch>
//
// bitswitch.header():
// one = const 1
// shifted = one << switchval.unsigned
// bitmask1 = const <bitmask1>
// switch (shifted & bitmask1)
// 0 -> bitswitch.case2()
// default -> <case1Branch>
//
// bitswitch.case2():
// bitmask2 = const <bitmask2>
// switch (shifted & bitmask1)
// 0 -> bitswitch.case3()
// default -> <case2Branch>
//
// ...
var entryBlock = graph.AddBasicBlock("bitswitch.entry");
var headerBlock = graph.AddBasicBlock("bitswitch.header");
var valueType = graph.GetValueType(value);
var valueSpec = valueType.GetIntegerSpecOrNull();
var defaultBranch = Flow.DefaultBranch;
// Subtract the min value from the switch value if necessary.
if (!MinValue.IsZero)
{
value = entryBlock.AppendInstruction(
Instruction.CreateBinaryArithmeticIntrinsic(
ArithmeticIntrinsics.Operators.Subtract,
false,
valueType,
value,
entryBlock.AppendInstruction(
Instruction.CreateConstant(MinValue, valueType),
"minvalue")),
"switchval.adjusted");
}
// Make the switch value unsigned if it wasn't already.
if (valueSpec.IsSigned)
{
var uintType = TypeEnvironment.MakeUnsignedIntegerType(valueSpec.Size);
value = entryBlock.AppendInstruction(
Instruction.CreateConvertIntrinsic(
false,
uintType,
valueType,
value),
"switchval.unsigned");
valueType = uintType;
valueSpec = uintType.GetIntegerSpecOrNull();
}
// Check that the value is within range.
entryBlock.Flow = SwitchFlow.CreateIfElse(
Instruction.CreateRelationalIntrinsic(
ArithmeticIntrinsics.Operators.IsGreaterThan,
TypeEnvironment.Boolean,
valueType,
value,
entryBlock.AppendInstruction(
Instruction.CreateConstant(
ValueRange.CastSignedness(false),
valueType),
"valrange")),
defaultBranch,
new Branch(headerBlock));
// Pick an appropriate type for the bitmasks.
var bitmaskType = valueType;
if (valueSpec.Size < 32)
{
bitmaskType = TypeEnvironment.UInt32;
}
if (ValueRange.IsGreaterThan(new IntegerConstant(valueSpec.Size, ValueRange.Spec)))
{
bitmaskType = TypeEnvironment.UInt64;
}
// Set up first part of the header block.
if (bitmaskType != valueType)
{
valueSpec = bitmaskType.GetIntegerSpecOrNull();
}
var zero = headerBlock.AppendInstruction(
Instruction.CreateConstant(
new IntegerConstant(0, valueSpec),
valueType),
"zero");
var one = headerBlock.AppendInstruction(
Instruction.CreateConstant(
new IntegerConstant(1, valueSpec),
valueType),
"one");
value = headerBlock.AppendInstruction(
Instruction.CreateArithmeticIntrinsic(
ArithmeticIntrinsics.Operators.LeftShift,
false,
bitmaskType,
new[] { bitmaskType, valueType },
new[] { one, value }),
"shifted");
valueType = bitmaskType;
// Start emitting cases.
var caseBlock = headerBlock;
var nextCase = graph.AddBasicBlock("bitswitch.case1");
for (int i = 0; i < Flow.Cases.Count; i++)
{
// Construct a mask for the case.
var switchCase = Flow.Cases[i];
var oneConstant = new IntegerConstant(1, valueSpec);
var mask = new IntegerConstant(0, valueSpec);
foreach (var pattern in switchCase.Values)
{
mask = mask.BitwiseOr(oneConstant.ShiftLeft(((IntegerConstant)pattern).Subtract(MinValue)));
}
// Switch on the bitwise 'and' of the mask and
// the shifted value.
caseBlock.Flow = SwitchFlow.CreateIfElse(
Instruction.CreateBinaryArithmeticIntrinsic(
ArithmeticIntrinsics.Operators.And,
false,
valueType,
value,
caseBlock.AppendInstruction(
Instruction.CreateConstant(mask, valueType),
"bitmask" + i)),
switchCase.Branch,
new Branch(nextCase));
caseBlock = nextCase;
nextCase = graph.AddBasicBlock("bitswitch.case" + (i + 2));
}
// Jump to the default branch if nothing matches.
caseBlock.Flow = new JumpFlow(defaultBranch);
// Jump to the header block and let it do all of the heavy
// lifting.
return(new JumpFlow(entryBlock));
}
