[shader] add scalar control flow graph

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/SharpEmu.ShaderCompiler/Ir/IrControlFlow.cs

@@ -0,0 +1,161 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Collections.Generic;
+using System.Linq;
+
+namespace SharpEmu.ShaderCompiler.Ir;
+
+public readonly record struct IrBlockRange(uint StartPc, uint EndPc);
+
+public sealed class IrControlFlowGraph
+{
+    private IrControlFlowGraph(
+        IReadOnlyList<IrBlockRange> blocks,
+        IReadOnlyDictionary<uint, int> blockByStartPc,
+        IReadOnlyList<IReadOnlyList<int>> successors,
+        IReadOnlyList<IReadOnlyList<int>> predecessors,
+        IReadOnlySet<int> loopHeaders)
+    {
+        Blocks = blocks;
+        BlockByStartPc = blockByStartPc;
+        Successors = successors;
+        Predecessors = predecessors;
+        LoopHeaders = loopHeaders;
+    }
+
+    public IReadOnlyList<IrBlockRange> Blocks { get; }
+
+    public IReadOnlyDictionary<uint, int> BlockByStartPc { get; }
+
+    public IReadOnlyList<IReadOnlyList<int>> Successors { get; }
+
+    public IReadOnlyList<IReadOnlyList<int>> Predecessors { get; }
+
+    public IReadOnlySet<int> LoopHeaders { get; }
+
+    public bool HasControlFlow => Blocks.Count > 1;
+
+    public static IrControlFlowGraph Build(
+        IReadOnlyList<Gen5ShaderInstruction> instructions,
+        IIrBranchResolver resolver)
+    {
+        var leaders = new SortedSet<uint>();
+        if (instructions.Count > 0)
+        {
+            leaders.Add(instructions[0].Pc);
+        }
+
+        for (var index = 0; index < instructions.Count; index++)
+        {
+            var instruction = instructions[index];
+            if (!resolver.IsBranch(instruction))
+            {
+                continue;
+            }
+
+            if (resolver.TryGetBranchTarget(instruction, out var target))
+            {
+                leaders.Add(target);
+            }
+
+            if (index + 1 < instructions.Count)
+            {
+                leaders.Add(instructions[index + 1].Pc);
+            }
+        }
+
+        var ordered = leaders.ToList();
+        var ranges = new List<IrBlockRange>(ordered.Count);
+        var byStart = new Dictionary<uint, int>();
+        for (var index = 0; index < ordered.Count; index++)
+        {
+            var start = ordered[index];
+            var end = index + 1 < ordered.Count
+                ? ordered[index + 1]
+                : instructions.Count > 0 ? instructions[^1].Pc + 1 : start;
+            byStart[start] = ranges.Count;
+            ranges.Add(new IrBlockRange(start, end));
+        }
+
+        var successors = new List<List<int>>(ranges.Count);
+        var predecessors = new List<List<int>>(ranges.Count);
+        for (var index = 0; index < ranges.Count; index++)
+        {
+            successors.Add([]);
+            predecessors.Add([]);
+        }
+
+        for (var blockIndex = 0; blockIndex < ranges.Count; blockIndex++)
+        {
+            var range = ranges[blockIndex];
+            var last = instructions
+                .Where(candidate => candidate.Pc >= range.StartPc && candidate.Pc < range.EndPc)
+                .LastOrDefault();
+            if (last is null)
+            {
+                continue;
+            }
+
+            var isBranch = resolver.IsBranch(last);
+            var hasTarget = isBranch && resolver.TryGetBranchTarget(last, out var target) &&
+                byStart.TryGetValue(target, out var targetIndex);
+            if (hasTarget)
+            {
+                _ = resolver.TryGetBranchTarget(last, out var resolved);
+                Link(successors, predecessors, blockIndex, byStart[resolved]);
+            }
+
+            var fallsThrough = !isBranch || resolver.IsConditional(last);
+            if (fallsThrough && blockIndex + 1 < ranges.Count)
+            {
+                Link(successors, predecessors, blockIndex, blockIndex + 1);
+            }
+        }
+
+        var headers = new HashSet<int>();
+        for (var blockIndex = 0; blockIndex < ranges.Count; blockIndex++)
+        {
+            foreach (var successor in successors[blockIndex])
+            {
+                if (successor <= blockIndex)
+                {
+                    headers.Add(successor);
+                }
+            }
+        }
+
+        return new IrControlFlowGraph(
+            ranges,
+            byStart,
+            successors.Select(list => (IReadOnlyList<int>)list).ToList(),
+            predecessors.Select(list => (IReadOnlyList<int>)list).ToList(),
+            headers);
+    }
+
+    private static void Link(
+        List<List<int>> successors,
+        List<List<int>> predecessors,
+        int from,
+        int to)
+    {
+        if (!successors[from].Contains(to))
+        {
+            successors[from].Add(to);
+        }
+
+        if (!predecessors[to].Contains(from))
+        {
+            predecessors[to].Add(from);
+        }
+    }
+}
+
+public interface IIrBranchResolver
+{
+    bool IsBranch(Gen5ShaderInstruction instruction);
+
+    bool IsConditional(Gen5ShaderInstruction instruction);
+
+    bool TryGetBranchTarget(Gen5ShaderInstruction instruction, out uint targetPc);
+}