From 67d27dbe631d1292be363f4121217d66e2d7fd0f Mon Sep 17 00:00:00 2001
From: Luuk de Gram <luuk@degram.dev>
Date: Sat, 6 May 2023 17:46:51 +0200
Subject: [PATCH] wasm: fix liveness bugs

Make sure to increase the reference count for `intcast` when the
operand doesn't require any casting of the respective WebAssembly type.

Function arguments have a reserved slot, and therefore cannot be
re-used arbitrarily
---
 src/arch/wasm/CodeGen.zig | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/arch/wasm/CodeGen.zig b/src/arch/wasm/CodeGen.zig
index 799c4a40a2e983d7ceccefd84e0549ff5730a4ed..c2d2ffd8e40cdb9fe7c36818415c1655a0a4b58d 100644
--- a/src/arch/wasm/CodeGen.zig
+++ b/src/arch/wasm/CodeGen.zig
@@ -881,6 +881,9 @@ fn processDeath(func: *CodeGen, ref: Air.Inst.Ref) void {
     const value = func.currentBranch().values.getPtr(ref) orelse return;
     if (value.* != .local) return;
     log.debug("Decreasing reference for ref: %{?d}\n", .{Air.refToIndex(ref)});
+    if (value.local.value < func.arg_index) {
+        return; // function arguments can never be re-used
+    }
     value.local.references -= 1; // if this panics, a call to `reuseOperand` was forgotten by the developer
     if (value.local.references == 0) {
         value.free(func);
@@ -4021,7 +4024,13 @@ fn airIntcast(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
         return func.fail("todo Wasm intcast for bitsize > 128", .{});
     }
 
-    const result = try (try func.intcast(operand, operand_ty, ty)).toLocal(func, ty);
+    const op_bits = toWasmBits(@intCast(u16, ty.bitSize(func.target))).?;
+    const wanted_bits = toWasmBits(@intCast(u16, ty.bitSize(func.target))).?;
+    const result = if (op_bits == wanted_bits)
+        func.reuseOperand(ty_op.operand, operand)
+    else
+        try (try func.intcast(operand, operand_ty, ty)).toLocal(func, ty);
+
     func.finishAir(inst, result, &.{});
 }
 
-- 
2.54.0