diff --git a/src/arm-codegen.c b/src/arm-codegen.c
index 1290c091..fd1303b9 100644
--- a/src/arm-codegen.c
+++ b/src/arm-codegen.c
@@ -410,7 +410,7 @@ void code_generate()
             emit(__mov_i(__EQ, rd, 1));
             break;
         case OP_log_and:
-            /* FIXME: bad-logical instruction */
+            /* FIXME: bad logical-and instruction */
             emit(__and_r(__AL, rd, rn, rm));
             break;
         case OP_log_or:
diff --git a/src/cfront.c b/src/cfront.c
index b7523d6c..8ce74aae 100644
--- a/src/cfront.c
+++ b/src/cfront.c
@@ -1016,7 +1016,10 @@ void read_func_parameters(block_t *parent, basic_block_t **bb)
     for (i = 0; i < param_num; i++) {
         ph1_ir_t *ph1_ir = add_ph1_ir(OP_push);
         ph1_ir->src0 = params[i];
-        /* Liveness extension in allocation uses `param_num - i` */
+        /**
+         * The operand should keep alive before calling function. Pass the
+         * number of remained parameters to allocator to extend their liveness.
+         */
         add_inst(parent, *bb, OP_push, NULL, ph1_ir->src0, NULL, param_num - i,
                  NULL);
     }
diff --git a/src/reg-alloc.c b/src/reg-alloc.c
index 489172a3..720ad0f8 100644
--- a/src/reg-alloc.c
+++ b/src/reg-alloc.c
@@ -203,6 +203,9 @@ void spill_live_out(basic_block_t *bb)
     }
 }
 
+/**
+ * The operand of `OP_push` should not been killed until function called.
+ */
 void extend_liveness(basic_block_t *bb, Inst_t *inst, var_t *var, int offset)
 {
     if (check_live_out(bb, var))
@@ -351,7 +354,7 @@ void reg_alloc()
                     ir->dest = dest;
                     break;
                 case OP_address_of:
-                    /* FIXME: indirect assignment of pointer */
+                    /* make sure variable is on stack */
                     if (!inst->rs1->offset) {
                         inst->rs1->offset = bb->belong_to->func->stack_size;
                         bb->belong_to->func->stack_size += 4;
@@ -377,7 +380,7 @@ void reg_alloc()
                     ir->src0 = src0;
                     ir->dest = dest;
 
-                    /* store global variable after assignment immediately */
+                    /* store global variable immediately after assignment */
                     if (inst->rd->is_global) {
                         ir = bb_add_ph2_ir(bb, OP_global_store);
                         ir->src0 = dest;
@@ -386,7 +389,6 @@ void reg_alloc()
                     }
                     break;
                 case OP_read:
-                    /* FIXME: indirect assignment of pointer */
                     src0 = prepare_operand(bb, inst->rs1, -1);
                     dest = prepare_dest(bb, inst->rd, src0, -1);
                     ir = bb_add_ph2_ir(bb, OP_read);
@@ -401,7 +403,8 @@ void reg_alloc()
                         ir->src0 = src0;
                         strcpy(ir->func_name, inst->rs2->var_name);
                     } else {
-                        /* FIXME: indirect assignment of pointer */
+                        /* FIXME: Avoid outdated content in register after
+                         * storing, but causing some redundant spilling. */
                         spill_alive(bb, inst);
                         src0 = prepare_operand(bb, inst->rs1, -1);
                         src1 = prepare_operand(bb, inst->rs2, src0);
@@ -561,7 +564,6 @@ void reg_alloc()
     }
 }
 
-/* not support "%c" in printf() yet */
 void dump_ph2_ir()
 {
     ph2_ir_t *ph2_ir;
diff --git a/src/ssa.c b/src/ssa.c
index 5f82375c..57698700 100644
--- a/src/ssa.c
+++ b/src/ssa.c
@@ -530,7 +530,7 @@ void solve_phi_params()
     for (fn = FUNC_LIST.head; fn; fn = fn->next) {
         int i;
         for (i = 0; i < fn->func->num_params; i++) {
-            /* FIXME: Directly rename parameters, might be not good here. */
+            /* FIXME: Rename arguments directly, might be not good here. */
             var_t *var = require_var(fn->bbs->scope);
             var_t *base = &fn->func->param_defs[i];
             memcpy(var, base, sizeof(var_t));
@@ -583,7 +583,7 @@ void bb_unwind_phi(fn_t *fn, basic_block_t *bb)
         for (operand = inst->phi_ops; operand; operand = operand->next) {
             append_unwound_phi_inst(operand->from, inst->rd, operand->var);
         }
-        /* TODO: Should release phi instructions */
+        /* TODO: Release dangling phi instruction */
     }
 
     bb->inst_list.head = inst;