Reduce size of GC object header

4 files changed, 45 insertions, 16 deletions

diff --git a/src/main/java/org/shedlang/compiler/backends/llvm/codegen/PatioToLlvm.java b/src/main/java/org/shedlang/compiler/backends/llvm/codegen/PatioToLlvm.java
index 104080be..859d79ab 100644
--- a/src/main/java/org/shedlang/compiler/backends/llvm/codegen/PatioToLlvm.java
+++ b/src/main/java/org/shedlang/compiler/backends/llvm/codegen/PatioToLlvm.java
@@ -189,7 +189,7 @@ public class PatioToLlvm {
                 context.target()
             )),
             true,
-            true,
+            false,
             true
         ));
     }
diff --git a/src/main/java/org/shedlang/compiler/shidtopatio/ScalarRuntimeType.java b/src/main/java/org/shedlang/compiler/shidtopatio/ScalarRuntimeType.java
new file mode 100644
index 00000000..27a8dd4b
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/shidtopatio/ScalarRuntimeType.java
@@ -0,0 +1,29 @@
+package org.shedlang.compiler.shidtopatio;
+
+import org.shedlang.compiler.patio.types.PatioDataLayout;
+import org.shedlang.compiler.patio.types.PatioDataLayouts;
+
+import java.util.List;
+
+public class ScalarRuntimeType implements RuntimeType {
+    public static final ScalarRuntimeType INSTANCE = new ScalarRuntimeType();
+
+    private ScalarRuntimeType() {
+    }
+
+    @Override
+    public PatioDataLayout layout() {
+        // TODO: separate out runtime type from the info needed by RTTI
+        return PatioDataLayouts.struct(List.of());
+    }
+
+    @Override
+    public List<Integer> gcChildrenOffset() {
+        return List.of();
+    }
+
+    @Override
+    public int gcChildrenCount() {
+        return 0;
+    }
+}
diff --git a/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioContext.java b/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioContext.java
index dd187acc..04644052 100644
--- a/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioContext.java
+++ b/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioContext.java
@@ -42,12 +42,18 @@ public record ShidToPatioContext(
             var effectTags = generateEffectTags(typeInfos);
             var runtimeTypeTags = P.<RuntimeType, Integer>orderedPMap();
 
-            return new GlobalContext(
+            var context = new GlobalContext(
                 typeInfos,
                 structTags,
                 effectTags,
                 runtimeTypeTags
             );
+
+            // Ensure that scalars have tag of 0: this is relied on in the
+            // runtime (for instance, when allocating ints and strings).
+            context = context.addRuntimeTypeTag(ScalarRuntimeType.INSTANCE);
+
+            return context;
         }
 
         @CheckReturnValue
@@ -116,12 +122,12 @@ public record ShidToPatioContext(
         }
 
         @CheckReturnValue
-        private GlobalContext addRuntimeTypeTag(RuntimeType runtimeType, Integer tag) {
+        private GlobalContext addRuntimeTypeTag(RuntimeType runtimeType) {
             return new GlobalContext(
                 this.typeInfos,
                 this.structTags,
                 this.effectTags,
-                this.runtimeTypeTags.plus(runtimeType, tag)
+                this.runtimeTypeTags.plus(runtimeType, this.runtimeTypeTags.size())
             );
         }
 
@@ -129,7 +135,7 @@ public record ShidToPatioContext(
         public Result<Integer> runtimeTypeTag(RuntimeType runtimeType) {
             var globalContext = this.runtimeTypeTags.containsKey(runtimeType)
                 ? this
-                : this.addRuntimeTypeTag(runtimeType, this.runtimeTypeTags.size());
+                : this.addRuntimeTypeTag(runtimeType);
 
             return globalContext.toResult(globalContext.runtimeTypeTags.get(runtimeType));
         }
diff --git a/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioGc.java b/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioGc.java
index 4d62f082..dff665f9 100644
--- a/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioGc.java
+++ b/src/main/java/org/shedlang/compiler/shidtopatio/ShidToPatioGc.java
@@ -7,7 +7,6 @@ import org.shedlang.compiler.patio.instructions.PatioMemoryStore;
 import org.shedlang.compiler.patio.operands.*;
 import org.shedlang.compiler.patio.types.*;
 import org.shedlang.compiler.patio.values.PatioDataPtrValueNull;
-import org.shedlang.compiler.patio.values.PatioIntValueByteOffsetOf;
 import org.shedlang.compiler.patio.values.PatioIntValueByteSizeOf;
 import org.shedlang.compiler.sources.Source;
 import org.shedlang.compiler.sources.Sources;
@@ -25,9 +24,8 @@ public class ShidToPatioGc {
         return PatioDataLayouts.struct(List.of(
             PatioDataLayouts.struct(List.of(
                 PatioDataLayouts.DATA_PTR, // next
-                PatioDataLayouts.INT, // mark
-                PatioDataLayouts.INT32, // children offset
-                PatioDataLayouts.INT32 // children count
+                PatioDataLayouts.INT32, // mark
+                PatioDataLayouts.INT32 // runtime type tag
             )),
             valueLayout
         ));
@@ -47,8 +45,7 @@ public class ShidToPatioGc {
             PatioDataValues.struct(List.of(
                 PatioDataValues.int_(0),
                 // Static values are always marked: see gc.c
-                PatioDataValues.int_(0b110),
-                PatioDataValues.int32(0),
+                PatioDataValues.int32(0b110),
                 PatioDataValues.int32(0)
             )),
             value
@@ -131,8 +128,7 @@ public class ShidToPatioGc {
         "shed__runtime__gc_alloc",
         List.of(
             PatioLocal.param("size", PatioTypes.INT),
-            PatioLocal.param("children_offset", PatioTypes.INT32),
-            PatioLocal.param("children_count", PatioTypes.INT32)
+            PatioLocal.param("runtime_type_tag", PatioTypes.INT32)
         ),
         PatioTypes.DATA_PTR,
         Sources.RUNTIME
@@ -156,12 +152,10 @@ public class ShidToPatioGc {
 
         var size = new PatioIntConst(new PatioIntValueByteSizeOf(layout));
 
-        var offset = new PatioInt32Const(new PatioIntValueByteOffsetOf(layout, childrenOffset));
-
         context = context.addInstruction(new PatioCall(
             Optional.of(destination),
             ALLOC.name(),
-            List.of(size, offset, PatioInt32Const.of(childrenCount)),
+            List.of(size, PatioInt32Const.of(runtimeTypeTag)),
             source
         ));