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, 24 insertions, 4 deletions

diff --git a/src/shader_recompiler/backend/glasm/reg_alloc.cpp b/src/shader_recompiler/backend/glasm/reg_alloc.cpp
index 707b22247a..c55a833c6d 100644
--- a/src/shader_recompiler/backend/glasm/reg_alloc.cpp
+++ b/src/shader_recompiler/backend/glasm/reg_alloc.cpp
@@ -22,11 +22,19 @@ Register RegAlloc::LongDefine(IR::Inst& inst) {
 }
 
 Value RegAlloc::Peek(const IR::Value& value) {
-    return value.IsImmediate() ? MakeImm(value) : PeekInst(*value.InstRecursive());
+    if (value.IsImmediate()) {
+        return MakeImm(value);
+    } else {
+        return PeekInst(*value.Inst());
+    }
 }
 
 Value RegAlloc::Consume(const IR::Value& value) {
-    return value.IsImmediate() ? MakeImm(value) : ConsumeInst(*value.InstRecursive());
+    if (value.IsImmediate()) {
+        return MakeImm(value);
+    } else {
+        return ConsumeInst(*value.Inst());
+    }
 }
 
 void RegAlloc::Unref(IR::Inst& inst) {
@@ -88,7 +96,14 @@ Value RegAlloc::MakeImm(const IR::Value& value) {
 }
 
 Register RegAlloc::Define(IR::Inst& inst, bool is_long) {
-    inst.SetDefinition<Id>(Alloc(is_long));
+    if (inst.HasUses()) {
+        inst.SetDefinition<Id>(Alloc(is_long));
+    } else {
+        Id id{};
+        id.is_long.Assign(is_long ? 1 : 0);
+        id.is_null.Assign(1);
+        inst.SetDefinition<Id>(id);
+    }
     return Register{PeekInst(inst)};
 }
 
@@ -115,10 +130,12 @@ Id RegAlloc::Alloc(bool is_long) {
             num_regs = std::max(num_regs, reg + 1);
             use[reg] = true;
             Id ret{};
-            ret.index.Assign(static_cast<u32>(reg));
+            ret.is_valid.Assign(1);
             ret.is_long.Assign(is_long ? 1 : 0);
             ret.is_spill.Assign(0);
             ret.is_condition_code.Assign(0);
+            ret.is_null.Assign(0);
+            ret.index.Assign(static_cast<u32>(reg));
             return ret;
         }
     }
@@ -126,6 +143,9 @@ Id RegAlloc::Alloc(bool is_long) {
 }
 
 void RegAlloc::Free(Id id) {
+    if (id.is_valid == 0) {
+        throw LogicError("Freeing invalid register");
+    }
     if (id.is_spill != 0) {
         throw NotImplementedException("Free spill");
     }