wasm: fix bitcasting to -and from arrays

Arrays are currently always passed by reference, this means that we
always keep the value in linear memory and never load it to Wasm's
stack. Scalar values however do get lowered to Wasm's stack.
This means when bitcasting from an array to a scalar value, we must
load the memory of the array as such scalar type. To bitcast
a scalar type to an array, we allocate a new temporary in the
linear data segment, and then store the scalar value there.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/arch/wasm/CodeGen.zig b/src/arch/wasm/CodeGen.zig
index 9da4d3003b..21ddd91120 100644
--- a/src/arch/wasm/CodeGen.zig
+++ b/src/arch/wasm/CodeGen.zig
@@ -3814,6 +3814,16 @@ fn airBitcast(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
             const bitcast_result = try func.bitcast(wanted_ty, given_ty, operand);
             break :result try bitcast_result.toLocal(func, wanted_ty);
         }
+        const mod = func.bin_file.base.options.module.?;
+        if (isByRef(given_ty, mod) and !isByRef(wanted_ty, mod)) {
+            const loaded_memory = try func.load(operand, wanted_ty, 0);
+            break :result try loaded_memory.toLocal(func, wanted_ty);
+        }
+        if (!isByRef(given_ty, mod) and isByRef(wanted_ty, mod)) {
+            const stack_memory = try func.allocStack(wanted_ty);
+            try func.store(stack_memory, operand, given_ty, 0);
+            break :result stack_memory;
+        }
         break :result func.reuseOperand(ty_op.operand, operand);
     };
     func.finishAir(inst, result, &.{ty_op.operand});