Fix reference reads for pointer-represented values

Author: wtholliday

ref_struct_stack_crash.lyte

@@ -0,0 +1,26 @@
+// Minimal repro for stack backend handling of reference parameters to structs.
+// Expected behavior: both stack and LLVM finish successfully.
+// Observed with lyte rev 1e780c772cbf68eeec7584a188d16eb24b5ca830:
+//   --backend llvm  finishes successfully
+//   --backend stack exits abruptly with code -1 and no diagnostic
+
+struct Grain {
+  phase: f32,
+  gain: f32
+}
+
+process_grain(grain: &Grain, amount: f32) -> f32 {
+  grain.phase = grain.phase + amount
+  grain.gain = grain.gain * 2.0
+  grain.phase + grain.gain
+}
+
+main {
+  var grain: Grain
+  grain.phase = 1.0
+  grain.gain = 2.0
+  let out = process_grain(grain, 1.0)
+  assert(out == 6.0)
+  assert(grain.phase == 2.0)
+  assert(grain.gain == 4.0)
+}

src/stack_codegen.rs

@@ -1066,7 +1066,9 @@ impl<'a> FunctionTranslator<'a> {
                 }
                 LocalKind::Reference(slot) => {
                     func.emit(StackOp::LocalGet(slot));
-                    self.emit_load(&ty, func);
+                    if !self.is_ptr_type(&ty) {
+                        self.emit_load(&ty, func);
+                    }
                 }
                 LocalKind::Memory(slot) => {
                     if self.is_ptr_type(&ty) {

src/vm_codegen.rs

@@ -882,6 +882,9 @@ impl<'a> FunctionTranslator<'a> {
                 // Check if it's a local variable.
                 if let Some(&reg) = self.variables.get(name) {
                     if self.reference_vars.contains(name) {
+                        if self.is_ptr_type(&ty) {
+                            return reg;
+                        }
                         let dst = self.alloc_reg();
                         self.emit_load(&ty, dst, reg, func);
                         dst

tests/cases/references/ref_struct_param.lyte

@@ -0,0 +1,26 @@
+// expected stdout:
+// compilation successful
+// assert(true)
+// assert(true)
+// assert(true)
+
+struct Grain {
+  phase: f32,
+  gain: f32
+}
+
+process_grain(grain: &Grain, amount: f32) -> f32 {
+  grain.phase = grain.phase + amount
+  grain.gain = grain.gain * 2.0
+  grain.phase + grain.gain
+}
+
+main {
+  var grain: Grain
+  grain.phase = 1.0
+  grain.gain = 2.0
+  let out = process_grain(grain, 1.0)
+  assert(out == 6.0)
+  assert(grain.phase == 2.0)
+  assert(grain.gain == 4.0)
+}