simplify: port IntConvert to C via SimplifyEnv (chunk 7)

simplify_int_convert_c: if src already has target type, emits
UseType and returns src unchanged. Uses HirIntConvert struct's
type field directly (same layout as HirRefineType).

Author: SonicField

Python/jit/hir/simplify.cpp

@@ -2763,8 +2763,12 @@ Register* simplifyInstr(Env& env, const Instr* instr) {
     case Opcode::kGetLength:
       return simplifyGetLength(env, instr);
 
-    case Opcode::kIntConvert:
-      return simplifyIntConvert(env, static_cast<const IntConvert*>(instr));
+    case Opcode::kIntConvert: {
+      SimplifyEnv cenv = make_c_env();
+      auto *r = static_cast<Register*>(simplify_int_convert_c(&cenv, instr));
+      sync_c_env(cenv);
+      return r;
+    }
 
     case Opcode::kIsTruthy:
       return simplifyIsTruthy(env, instr);

Python/jit/hir/simplify_c.c

@@ -89,6 +89,19 @@ void *simplify_cint_to_cbool_c(SimplifyEnv *env, const void *instr) {
     return NULL;
 }
 
+/* ---- simplifyIntConvert ----
+ * If input already has the target type, IntConvert is redundant. */
+void *simplify_int_convert_c(SimplifyEnv *env, const void *instr) {
+    void *src = hir_c_get_operand(instr, 0);
+    HirType src_type = hir_register_type(src);
+    HirType target = ((const HirIntConvert *)instr)->type;
+    if (hir_type_is_subtype(src_type, target)) {
+        simplify_env_emit_use_type(env, src, target);
+        return src;
+    }
+    return NULL;
+}
+
 /* ---- simplifyCondBranch (partial — constant condition folding) ----
  * If condition is a known int constant, fold to unconditional Branch. */
 void *simplify_cond_branch_const_c(SimplifyEnv *env, const void *instr) {

Python/jit/hir/simplify_c.h

@@ -29,6 +29,7 @@ void *simplify_env_emit_use_type(SimplifyEnv *env, void *val, HirType type);
 void *simplify_check_c(const void *instr);
 void *simplify_refine_type_c(const void *instr);
 void *simplify_guard_type_identity_c(const void *instr);
+void *simplify_int_convert_c(SimplifyEnv *env, const void *instr);
 
 /* Env-using handlers (Category 2) */
 void *simplify_primitive_box_bool_c(SimplifyEnv *env, const void *instr);