Shaders: Implemented a stack for the SSY/SYNC instructions.

The SSY instruction pushes an address into the stack, and the SYNC instruction pops it. The current stack depth is 20, we should figure out if this is enough or not.

src/video_core/renderer_opengl/gl_shader_decompiler.cpp

@@ -815,6 +815,33 @@ private:
         shader.AddLine('}');
     }
 
+    /*
+     * Emits code to push the input target address to the SSY address stack, incrementing the stack
+     * top.
+     */
+    void EmitPushToSSYStack(u32 target) {
+        shader.AddLine('{');
+        ++shader.scope;
+        shader.AddLine("ssy_stack[ssy_stack_top] = " + std::to_string(target) + "u;");
+        shader.AddLine("ssy_stack_top++;");
+        --shader.scope;
+        shader.AddLine('}');
+    }
+
+    /*
+     * Emits code to pop an address from the SSY address stack, setting the jump address to the
+     * popped address and decrementing the stack top.
+     */
+    void EmitPopFromSSYStack() {
+        shader.AddLine('{');
+        ++shader.scope;
+        shader.AddLine("ssy_stack_top--;");
+        shader.AddLine("jmp_to = ssy_stack[ssy_stack_top];");
+        shader.AddLine("break;");
+        --shader.scope;
+        shader.AddLine('}');
+    }
+
     /**
      * Compiles a single instruction from Tegra to GLSL.
      * @param offset the offset of the Tegra shader instruction.
@@ -1843,13 +1870,13 @@ private:
                 ASSERT_MSG(instr.bra.constant_buffer == 0, "Constant buffer SSY is not supported");
 
                 u32 target = offset + instr.bra.GetBranchTarget();
-                shader.AddLine("ssy_target = " + std::to_string(target) + "u;");
+                EmitPushToSSYStack(target);
                 break;
             }
             case OpCode::Id::SYNC: {
                 // The SYNC opcode jumps to the address previously set by the SSY opcode
                 ASSERT(instr.flow.cond == Tegra::Shader::FlowCondition::Always);
-                shader.AddLine("{ jmp_to = ssy_target; break; }");
+                EmitPopFromSSYStack();
                 break;
             }
             case OpCode::Id::DEPBAR: {
@@ -1920,7 +1947,13 @@ private:
             } else {
                 labels.insert(subroutine.begin);
                 shader.AddLine("uint jmp_to = " + std::to_string(subroutine.begin) + "u;");
-                shader.AddLine("uint ssy_target = 0u;");
+
+                // TODO(Subv): Figure out the actual depth of the SSY stack, for now it seems
+                // unlikely that shaders will use 20 nested SSYs.
+                constexpr u32 SSY_STACK_SIZE = 20;
+                shader.AddLine("uint ssy_stack[" + std::to_string(SSY_STACK_SIZE) + "];");
+                shader.AddLine("uint ssy_stack_top = 0u;");
+
                 shader.AddLine("while (true) {");
                 ++shader.scope;