glasm: Catch more register leaks

Add support for null registers. These are used when an instruction has
no usages.

This comes handy when an instruction is only used for its CC value, with
the caveat of having to invalidate all pseudo-instructions before
defining the instruction itself in the register allocator. This commits
changes this.

Workaround a bug on Nvidia's condition codes conditional execution using
branches.

1 files changed, 12 insertions, 4 deletions

diff --git a/src/shader_recompiler/backend/glasm/reg_alloc.h b/src/shader_recompiler/backend/glasm/reg_alloc.h
index 41b7c92be..b97c84146 100644
--- a/src/shader_recompiler/backend/glasm/reg_alloc.h
+++ b/src/shader_recompiler/backend/glasm/reg_alloc.h
@@ -35,10 +35,12 @@ 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 {
@@ -164,12 +166,18 @@ auto FormatTo(FormatContext& ctx, Id id) {
         throw NotImplementedException("Spill emission");
     }
     if constexpr (scalar) {
+        if (id.is_null != 0) {
+            return fmt::format_to(ctx.out(), "{}", id.is_long != 0 ? "DC.x" : "RC.x");
+        }
         if (id.is_long != 0) {
             return fmt::format_to(ctx.out(), "D{}.x", id.index.Value());
         } else {
             return fmt::format_to(ctx.out(), "R{}.x", id.index.Value());
         }
     } else {
+        if (id.is_null != 0) {
+            return fmt::format_to(ctx.out(), "{}", id.is_long != 0 ? "DC" : "RC");
+        }
         if (id.is_long != 0) {
             return fmt::format_to(ctx.out(), "D{}", id.index.Value());
         } else {