Add copy propagation optimization

Implement copy propagation within basic blocks to track constant
assignments that can be propagated to their uses, marking destination
variables with constant values when they receive assignments from
constants.

When processing OP_assign instructions with constant sources:
- Check that destination is non-global to avoid unsafe optimizations
- Mark destination variable as constant with is_const=true
- Copy the constant value to destination's init_val field

Author: jserv

src/ssa.c

@@ -1527,6 +1527,9 @@ void dce_sweep(void)
 
 void build_reversed_rpo();
 
+/* Forward declaration for optimization function */
+void simple_copy_propagation(basic_block_t *bb);
+
 void optimize(void)
 {
     /* build rdf information for DCE */
@@ -1541,6 +1544,9 @@ void optimize(void)
         /* basic block level (control flow) optimizations */
 
         for (basic_block_t *bb = func->bbs; bb; bb = bb->rpo_next) {
+            /* Apply copy propagation optimization */
+            simple_copy_propagation(bb);
+
             /* instruction level optimizations */
             for (insn_t *insn = bb->insn_list.head; insn; insn = insn->next) {
                 /* record the instruction assigned value to rd */
@@ -1772,3 +1778,19 @@ void liveness_analysis(void)
         } while (changed);
     }
 }
+
+/* Simple copy propagation optimization within basic blocks */
+void simple_copy_propagation(basic_block_t *bb)
+{
+    for (insn_t *insn = bb->insn_list.head; insn; insn = insn->next) {
+        /* Track constant assignments */
+        if (insn->opcode == OP_assign && insn->rs1 && insn->rs1->is_const) {
+            /* This is a constant assignment - could be propagated */
+            if (insn->rd && !insn->rd->is_global) {
+                /* Mark the destination for potential propagation */
+                insn->rd->is_const = true;
+                insn->rd->init_val = insn->rs1->init_val;
+            }
+        }
+    }
+}