Merge pull request #94 from vacantron/dev

Eliminate redundant branches
sysprog21 · Dec 16, 2023 · 9408e2b · 9408e2b
2 parents f8324c2 + aa336a2
commit 9408e2b
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Showing 3 changed files with 22 additions and 7 deletions.
diff --git a/src/arm-codegen.c b/src/arm-codegen.c
@@ -103,6 +103,11 @@ void update_elf_offset(ph2_ir_t *ph2_ir)
         elf_offset += 12;
         return;
     case OP_branch:
+        if (ph2_ir->is_branch_detached)
+            elf_offset += 12;
+        else
+            elf_offset += 8;
+        return;
     case OP_return:
         elf_offset += 24;
         return;
@@ -156,6 +161,12 @@ void cfg_flatten()
                     /* restore sp */
                     flatten_ir->src1 = bb->belong_to->func->stack_size;
 
+                if (insn->op == OP_branch) {
+                    /* In SSA, we index `else_bb` first, and then `then_bb` */
+                    if (insn->else_bb != bb->rpo_next)
+                        flatten_ir->is_branch_detached = 1;
+                }
+
                 update_elf_offset(flatten_ir);
             }
         }
@@ -264,13 +275,12 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
             abort();
         return;
     case OP_branch:
-        ofs = ph2_ir->else_bb->elf_offset;
-        emit(__movw(__AL, __r8, ofs + elf_code_start));
-        emit(__movt(__AL, __r8, ofs + elf_code_start));
         emit(__teq(rn));
-        emit(__b(__NE, 8));
-        emit(__blx(__AL, __r8));
-        emit(__b(__AL, ph2_ir->then_bb->elf_offset - elf_code_idx));
+        if (ph2_ir->is_branch_detached) {
+            emit(__b(__NE, 8));
+            emit(__b(__AL, ph2_ir->else_bb->elf_offset - elf_code_idx));
+        } else
+            emit(__b(__NE, ph2_ir->then_bb->elf_offset - elf_code_idx));
         return;
     case OP_jump:
         emit(__b(__AL, ph2_ir->next_bb->elf_offset - elf_code_idx));

diff --git a/src/defs.h b/src/defs.h
@@ -226,6 +226,7 @@ struct ph2_ir {
     basic_block_t *then_bb;
     basic_block_t *else_bb;
     struct ph2_ir *next;
+    int is_branch_detached;
 };
 
 typedef struct ph2_ir ph2_ir_t;

diff --git a/src/reg-alloc.c b/src/reg-alloc.c
@@ -287,6 +287,8 @@ void reg_alloc()
 
     fn_t *fn;
     for (fn = FUNC_LIST.head; fn; fn = fn->next) {
+        fn->visited++;
+
         if (!strcmp(fn->func->return_def.var_name, "main"))
             MAIN_BB = fn->bbs;
 
@@ -319,6 +321,8 @@ void reg_alloc()
         for (bb = fn->bbs; bb; bb = bb->rpo_next) {
             int is_pushing_args = 0, args = 0;
 
+            bb->visited++;
+
             insn_t *insn;
             for (insn = bb->insn_list.head; insn; insn = insn->next) {
                 ph2_ir_t *ir;
@@ -560,7 +564,7 @@ void reg_alloc()
 
             /* jump to the beginning of loop or over the else block */
             if (bb->next->visited == fn->visited ||
-                bb->next->visited != bb->rpo + 1) {
+                bb->next->rpo != bb->rpo + 1) {
                 ph2_ir_t *ir = bb_add_ph2_ir(bb, OP_jump);
                 ir->next_bb = bb->next;
             }