ShaderGen: Implemented predicated instruction execution.

Each predicated instruction will be wrapped in an `if (predicate) { instruction_body; }` in the GLSL, where `predicate` is one of the predicate boolean variables previously set by fsetp.

src/video_core/engines/shader_bytecode.h

@@ -331,7 +331,11 @@ union Instruction {
     OpCode opcode;
     BitField<0, 8, Register> gpr0;
     BitField<8, 8, Register> gpr8;
-    BitField<16, 4, Pred> pred;
+    union {
+        BitField<16, 4, Pred> full_pred;
+        BitField<16, 3, u64> pred_index;
+    } pred;
+    BitField<19, 1, u64> negate_pred;
     BitField<20, 8, Register> gpr20;
     BitField<20, 7, SubOp> sub_op;
     BitField<28, 8, Register> gpr28;

src/video_core/renderer_opengl/gl_shader_decompiler.cpp

@@ -293,6 +293,25 @@ private:
         declr_predicates.insert(std::move(variable));
     }
 
+    /*
+     * Returns the condition to use in the 'if' for a predicated instruction.
+     * @param instr Instruction to generate the if condition for.
+     * @returns string containing the predicate condition.
+     */
+    std::string GetPredicateCondition(Instruction instr) const {
+        using Tegra::Shader::Pred;
+        ASSERT(instr.pred.pred_index != static_cast<u64>(Pred::UnusedIndex));
+
+        std::string variable =
+            'p' + std::to_string(static_cast<u64>(instr.pred.pred_index.Value()));
+
+        if (instr.negate_pred) {
+            return "!(" + variable + ')';
+        }
+
+        return variable;
+    }
+
     /*
      * Returns whether the instruction at the specified offset is a 'sched' instruction.
      * Sched instructions always appear before a sequence of 3 instructions.
@@ -320,6 +339,16 @@ private:
 
         shader.AddLine("// " + std::to_string(offset) + ": " + OpCode::GetInfo(instr.opcode).name);
 
+        using Tegra::Shader::Pred;
+        ASSERT_MSG(instr.pred.full_pred != Pred::NeverExecute,
+                   "NeverExecute predicate not implemented");
+
+        if (instr.pred.pred_index != static_cast<u64>(Pred::UnusedIndex)) {
+            shader.AddLine("if (" + GetPredicateCondition(instr) + ')');
+            shader.AddLine('{');
+            ++shader.scope;
+        }
+
         switch (OpCode::GetInfo(instr.opcode).type) {
         case OpCode::Type::Arithmetic: {
             std::string dest = GetRegister(instr.gpr0);
@@ -559,6 +588,12 @@ private:
         }
         }
 
+        // Close the predicate condition scope.
+        if (instr.pred != Pred::UnusedIndex) {
+            --shader.scope;
+            shader.AddLine('}');
+        }
+
         return offset + 1;
     }