glsl: Update phi node management

src/shader_recompiler/backend/glsl/emit_glsl.cpp

@@ -98,18 +98,33 @@ void EmitInst(EmitContext& ctx, IR::Inst* inst) {
     throw LogicError("Invalid opcode {}", inst->GetOpcode());
 }
 
-void Precolor(EmitContext& ctx, const IR::Program& program) {
+bool IsReference(IR::Inst& inst) {
+    return inst.GetOpcode() == IR::Opcode::Reference;
+}
+
+void PrecolorInst(IR::Inst& phi) {
+    // Insert phi moves before references to avoid overwritting other phis
+    const size_t num_args{phi.NumArgs()};
+    for (size_t i = 0; i < num_args; ++i) {
+        IR::Block& phi_block{*phi.PhiBlock(i)};
+        auto it{std::find_if_not(phi_block.rbegin(), phi_block.rend(), IsReference).base()};
+        IR::IREmitter ir{phi_block, it};
+        const IR::Value arg{phi.Arg(i)};
+        if (arg.IsImmediate()) {
+            ir.PhiMove(phi, arg);
+        } else {
+            ir.PhiMove(phi, IR::Value{&RegAlloc::AliasInst(*arg.Inst())});
+        }
+    }
+    for (size_t i = 0; i < num_args; ++i) {
+        IR::IREmitter{*phi.PhiBlock(i)}.Reference(IR::Value{&phi});
+    }
+}
+
+void Precolor(const IR::Program& program) {
     for (IR::Block* const block : program.blocks) {
         for (IR::Inst& phi : block->Instructions() | std::views::take_while(IR::IsPhi)) {
-            ctx.Add("{};", ctx.reg_alloc.Define(phi, phi.Arg(0).Type()));
-            const size_t num_args{phi.NumArgs()};
-            for (size_t i = 0; i < num_args; ++i) {
-                IR::IREmitter{*phi.PhiBlock(i)}.PhiMove(phi, phi.Arg(i));
-            }
-            // Add reference to the phi node on the phi predecessor to avoid overwritting it
-            for (size_t i = 0; i < num_args; ++i) {
-                IR::IREmitter{*phi.PhiBlock(i)}.Reference(IR::Value{&phi});
-            }
+            PrecolorInst(phi);
         }
     }
 }
@@ -158,7 +173,7 @@ void EmitCode(EmitContext& ctx, const IR::Program& program) {
 std::string EmitGLSL(const Profile& profile, const RuntimeInfo&, IR::Program& program,
                      Bindings& bindings) {
     EmitContext ctx{program, bindings, profile};
-    Precolor(ctx, program);
+    Precolor(program);
     EmitCode(ctx, program);
     return ctx.code;
 }

src/shader_recompiler/backend/glsl/emit_glsl_not_implemented.cpp

@@ -19,8 +19,15 @@ static void NotImplemented() {
     throw NotImplementedException("GLSL instruction");
 }
 
-void EmitPhi(EmitContext& ctx, IR::Inst& inst) {
-    // NotImplemented();
+void EmitPhi(EmitContext& ctx, IR::Inst& phi) {
+    const size_t num_args{phi.NumArgs()};
+    for (size_t i = 0; i < num_args; ++i) {
+        ctx.reg_alloc.Consume(phi.Arg(i));
+    }
+    if (!phi.Definition<Id>().is_valid) {
+        // The phi node wasn't forward defined
+        ctx.Add("{};", ctx.reg_alloc.Define(phi, phi.Arg(0).Type()));
+    }
 }
 
 void EmitVoid(EmitContext& ctx) {
@@ -31,11 +38,18 @@ void EmitReference(EmitContext&) {
     // NotImplemented();
 }
 
-void EmitPhiMove(EmitContext& ctx, const IR::Value& phi, const IR::Value& value) {
-    if (phi == value) {
+void EmitPhiMove(EmitContext& ctx, const IR::Value& phi_value, const IR::Value& value) {
+    IR::Inst& phi{RegAlloc::AliasInst(*phi_value.Inst())};
+    if (!phi.Definition<Id>().is_valid) {
+        // The phi node wasn't forward defined
+        ctx.Add("{};", ctx.reg_alloc.Define(phi, phi.Arg(0).Type()));
+    }
+    const auto phi_reg{ctx.reg_alloc.Consume(IR::Value{&phi})};
+    const auto val_reg{ctx.reg_alloc.Consume(value)};
+    if (phi_reg == val_reg) {
         return;
     }
-    ctx.Add("{}={};", ctx.reg_alloc.Consume(phi), ctx.reg_alloc.Consume(value));
+    ctx.Add("{}={};", phi_reg, val_reg);
 }
 
 void EmitBranch(EmitContext& ctx, std::string_view label) {

src/shader_recompiler/backend/glsl/reg_alloc.cpp

@@ -146,10 +146,11 @@ Id RegAlloc::Alloc() {
             }
             register_use[reg] = true;
             Id ret{};
-            ret.index.Assign(static_cast<u32>(reg));
+            ret.is_valid.Assign(1);
             ret.is_long.Assign(0);
             ret.is_spill.Assign(0);
             ret.is_condition_code.Assign(0);
+            ret.index.Assign(static_cast<u32>(reg));
             return ret;
         }
     }

src/shader_recompiler/backend/glsl/reg_alloc.h

@@ -33,10 +33,12 @@ enum class Type : u32 {
 struct Id {
     union {
         u32 raw;
-        BitField<0, 29, u32> index;
-        BitField<29, 1, u32> is_long;
-        BitField<30, 1, u32> is_spill;
-        BitField<31, 1, u32> is_condition_code;
+        BitField<0, 1, u32> is_valid;
+        BitField<1, 1, u32> is_long;
+        BitField<2, 1, u32> is_spill;
+        BitField<3, 1, u32> is_condition_code;
+        BitField<4, 1, u32> is_null;
+        BitField<5, 27, u32> index;
     };
 
     bool operator==(Id rhs) const noexcept {