sema: fix cppcheck lint warnings

- autoVariables: heap-allocate cross-module source_dir copy instead of
  assigning pointer to local stack array
- identicalInnerCondition: simplify log2_int_ceil by removing redundant
  inner check (v > 0 always true when type_bits > 0)
- knownConditionTrueFalse: remove redundant !is_cross_module guard in
  else-if branch (always true since if-branch didn't execute)
- variableScope: narrow scope of di, field_name, ei variables
- unreadVariable: remove dead ei++ increment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

stage0/sema.c

@@ -2240,12 +2240,9 @@ static uint32_t findDeclInstByNameInZir(
         uint32_t payload = zir->inst_datas[di_inst].declaration.payload_index;
         uint32_t flags_1 = zir->extra[payload + 5];
         uint32_t id = (flags_1 >> 27) & 0x1F;
-        uint32_t di = payload + 6;
         uint32_t name_idx = 0;
-        if (declIdHasName(id)) {
-            name_idx = zir->extra[di];
-            di++;
-        }
+        if (declIdHasName(id))
+            name_idx = zir->extra[payload + 6];
         if (name_idx == 0)
             continue;
         const char* name = (const char*)&zir->string_bytes[name_idx];
@@ -2256,6 +2253,7 @@ static uint32_t findDeclInstByNameInZir(
 }
 
 // findFuncInstInZir: find a func/func_fancy instruction by name in a ZIR.
+
 // Scans the ZIR's struct_decl (inst 0) for a declaration matching the
 // given name, then searches its value body for a func instruction.
 // Uses the same parsing as zirStructDecl.
@@ -3103,12 +3101,12 @@ static AirInstRef zirCall(
             } else if (base_import && nfields == 1) {
                 // Single-level: e.g. const panic = common.panic;
                 // fields[0] = "panic"
-                const char* field_name = fields[0];
                 Ast base_ast;
                 memset(&base_ast, 0, sizeof(base_ast));
                 Zir base_zir = loadStdImportZir(sema->module_root,
                     sema->source_dir, base_import, &base_ast);
                 if (base_zir.inst_len > 0) {
+                    const char* field_name = fields[0];
                     func_inst = findFuncInstInZir(&base_zir, field_name);
                     if (func_inst != UINT32_MAX) {
                         saved_code = sema->code;
@@ -3364,9 +3362,8 @@ static AirInstRef zirCall(
                         //   field_val(decl_val("std"), "math"), "F80")
                         // callee_name = "fromFloat"
                         // Handles: std.math.F80.fromFloat(...)
-                    } else if (!is_cross_module
-                        && (lt == ZIR_INST_FIELD_VAL
-                            || lt == ZIR_INST_FIELD_PTR)) {
+                    } else if (lt == ZIR_INST_FIELD_VAL
+                        || lt == ZIR_INST_FIELD_PTR) {
                         uint32_t lp
                             = sema->code.inst_datas[li].pl_node.payload_index;
                         uint32_t lhs2_ref = sema->code.extra[lp];
@@ -4027,13 +4024,10 @@ static AirInstRef zirCall(
                 if (type_bits > 0) {
                     // log2_int_ceil: smallest n such that 2^n >= bits.
                     uint32_t n = 0;
-                    uint32_t v = type_bits;
-                    if (v > 0) {
-                        v--;
-                        while (v > 0) {
-                            n++;
-                            v >>= 1;
-                        }
+                    uint32_t v = type_bits - 1;
+                    while (v > 0) {
+                        n++;
+                        v >>= 1;
                     }
                     if (n == 0)
                         n = 1; // Log2Int minimum is u1
@@ -4619,7 +4613,11 @@ static AirInstRef zirCall(
         populateDeclTableFromZir(sema, &import_zir);
         if (import_source_dir[0]) {
             saved_source_dir = sema->source_dir;
-            sema->source_dir = import_source_dir;
+            size_t len = strlen(import_source_dir) + 1;
+            char* dir_copy = (char*)malloc(len);
+            assert(dir_copy);
+            memcpy(dir_copy, import_source_dir, len);
+            sema->source_dir = dir_copy;
         }
     }
 
@@ -4635,8 +4633,10 @@ static AirInstRef zirCall(
         memcpy(sema->decl_insts, saved_decl_insts,
             saved_num_decls * sizeof(uint32_t));
         sema->num_decls = saved_num_decls;
-        if (saved_source_dir)
+        if (saved_source_dir) {
+            free((char*)sema->source_dir);
             sema->source_dir = saved_source_dir;
+        }
     }
 
     sema->fn_ret_ty = saved_fn_ret_ty;
@@ -6620,10 +6620,9 @@ static bool analyzeBodyInner(
                 uint16_t small = sema->code.inst_datas[inst].extended.small;
                 uint32_t payload_index
                     = sema->code.inst_datas[inst].extended.operand;
-                uint32_t ei = payload_index + 1; // skip src_node
                 if (small & 0x1) { // has_type
+                    uint32_t ei = payload_index + 1; // skip src_node
                     ZirInstRef type_ref = sema->code.extra[ei];
-                    ei++;
                     AirInstRef resolved = resolveInst(sema, type_ref);
                     TypeIndex elem_ty = IP_INDEX_VOID_TYPE;
                     if (AIR_REF_IS_IP(resolved))