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using ARMeilleure.IntermediateRepresentation;
using ARMeilleure.Translation;
using System;
using System.Diagnostics;
using static ARMeilleure.IntermediateRepresentation.Operand.Factory;
namespace ARMeilleure.CodeGen.Optimizations
{
static class Optimizer
{
public static void RunPass(ControlFlowGraph cfg)
{
// Scratch buffer used to store uses.
Span<Operation> buffer = default;
bool modified;
do
{
modified = false;
for (BasicBlock block = cfg.Blocks.Last; block != null; block = block.ListPrevious)
{
Operation node;
Operation prevNode;
for (node = block.Operations.Last; node != default; node = prevNode)
{
prevNode = node.ListPrevious;
if (IsUnused(node))
{
RemoveNode(block, node);
modified = true;
continue;
}
else if (node.Instruction == Instruction.Phi)
{
continue;
}
ConstantFolding.RunPass(node);
Simplification.RunPass(node);
if (DestIsLocalVar(node))
{
if (IsPropagableCompare(node))
{
modified |= PropagateCompare(ref buffer, node);
if (modified && IsUnused(node))
{
RemoveNode(block, node);
}
}
else if (IsPropagableCopy(node))
{
PropagateCopy(ref buffer, node);
RemoveNode(block, node);
modified = true;
}
}
}
}
}
while (modified);
}
public static void RemoveUnusedNodes(ControlFlowGraph cfg)
{
bool modified;
do
{
modified = false;
for (BasicBlock block = cfg.Blocks.Last; block != null; block = block.ListPrevious)
{
Operation node;
Operation prevNode;
for (node = block.Operations.Last; node != default; node = prevNode)
{
prevNode = node.ListPrevious;
if (IsUnused(node))
{
RemoveNode(block, node);
modified = true;
}
}
}
}
while (modified);
}
private static Span<Operation> GetUses(ref Span<Operation> buffer, Operand operand)
{
ReadOnlySpan<Operation> uses = operand.Uses;
if (buffer.Length < uses.Length)
{
buffer = Allocators.Default.AllocateSpan<Operation>((uint)uses.Length);
}
uses.CopyTo(buffer);
return buffer.Slice(0, uses.Length);
}
private static bool PropagateCompare(ref Span<Operation> buffer, Operation compOp)
{
// Try to propagate Compare operations into their BranchIf uses, when these BranchIf uses are in the form
// of:
//
// - BranchIf %x, 0x0, Equal ;; i.e BranchIfFalse %x
// - BranchIf %x, 0x0, NotEqual ;; i.e BranchIfTrue %x
//
// The commutative property of Equal and NotEqual is taken into consideration as well.
//
// For example:
//
// %x = Compare %a, %b, comp
// BranchIf %x, 0x0, NotEqual
//
// =>
//
// BranchIf %a, %b, comp
static bool IsZeroBranch(Operation operation, out Comparison compType)
{
compType = Comparison.Equal;
if (operation.Instruction != Instruction.BranchIf)
{
return false;
}
Operand src1 = operation.GetSource(0);
Operand src2 = operation.GetSource(1);
Operand comp = operation.GetSource(2);
compType = (Comparison)comp.AsInt32();
return (src1.Kind == OperandKind.Constant && src1.Value == 0) ||
(src2.Kind == OperandKind.Constant && src2.Value == 0);
}
bool modified = false;
Operand dest = compOp.Destination;
Operand src1 = compOp.GetSource(0);
Operand src2 = compOp.GetSource(1);
Operand comp = compOp.GetSource(2);
Comparison compType = (Comparison)comp.AsInt32();
Span<Operation> uses = GetUses(ref buffer, dest);
foreach (Operation use in uses)
{
// If operation is a BranchIf and has a constant value 0 in its RHS or LHS source operands.
if (IsZeroBranch(use, out Comparison otherCompType))
{
Comparison propCompType;
if (otherCompType == Comparison.NotEqual)
{
propCompType = compType;
}
else if (otherCompType == Comparison.Equal)
{
propCompType = compType.Invert();
}
else
{
continue;
}
use.SetSource(0, src1);
use.SetSource(1, src2);
use.SetSource(2, Const((int)propCompType));
modified = true;
}
}
return modified;
}
private static void PropagateCopy(ref Span<Operation> buffer, Operation copyOp)
{
// Propagate copy source operand to all uses of the destination operand.
Operand dest = copyOp.Destination;
Operand source = copyOp.GetSource(0);
Span<Operation> uses = GetUses(ref buffer, dest);
foreach (Operation use in uses)
{
for (int index = 0; index < use.SourcesCount; index++)
{
if (use.GetSource(index) == dest)
{
use.SetSource(index, source);
}
}
}
}
private static void RemoveNode(BasicBlock block, Operation node)
{
// Remove a node from the nodes list, and also remove itself
// from all the use lists on the operands that this node uses.
block.Operations.Remove(node);
for (int index = 0; index < node.SourcesCount; index++)
{
node.SetSource(index, default);
}
Debug.Assert(node.Destination == default || node.Destination.UsesCount == 0);
node.Destination = default;
}
private static bool IsUnused(Operation node)
{
return DestIsLocalVar(node) && node.Destination.UsesCount == 0 && !HasSideEffects(node);
}
private static bool DestIsLocalVar(Operation node)
{
return node.Destination != default && node.Destination.Kind == OperandKind.LocalVariable;
}
private static bool HasSideEffects(Operation node)
{
return node.Instruction == Instruction.Call
|| node.Instruction == Instruction.Tailcall
|| node.Instruction == Instruction.CompareAndSwap
|| node.Instruction == Instruction.CompareAndSwap16
|| node.Instruction == Instruction.CompareAndSwap8;
}
private static bool IsPropagableCompare(Operation operation)
{
return operation.Instruction == Instruction.Compare;
}
private static bool IsPropagableCopy(Operation operation)
{
if (operation.Instruction != Instruction.Copy)
{
return false;
}
return operation.Destination.Type == operation.GetSource(0).Type;
}
}
}
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