Add fewer source blocks

Summary: If the split-off block already has a source block in the beginning, don't add another synthetic source block

Reviewed By: jimmycFB

Differential Revision: D57007595

fbshipit-source-id: 14c99ddd90a61980faa4fd6b1aded62788babae9

service/dedup-blocks/DedupBlocks.cpp

@@ -870,7 +870,10 @@ class DedupBlocksImpl {
             auto fwd_ir_it = IRList::iterator(std::prev(it.base()));
             split_block = cfg.split_block(block, fwd_ir_it);
           }
-          copy_over_source_block(block, split_block);
+          // add a source block in the beginning if there isn't one already
+          if (split_block->begin()->type != MFLOW_SOURCE_BLOCK) {
+            copy_over_source_block(block, split_block);
+          }
           continue;
         }
 
@@ -897,10 +900,13 @@ class DedupBlocksImpl {
         }
 
         auto cfg_it = block->to_cfg_instruction_iterator(fwd_it);
-        // Split the block
+        // Split the block and add a source block in the beginning if there
+        // isn't one already
         auto split_block = cfg.split_block(cfg_it);
+        if (split_block->begin()->type != MFLOW_SOURCE_BLOCK) {
+          copy_over_source_block(block, split_block);
+        }
 
-        copy_over_source_block(block, split_block);
         TRACE(DEDUP_BLOCKS, 4,
               "split_postfix: split block : old = %zu, new = %zu", block->id(),
               split_block->id());

test/integ/SourceBlocksDedupTest.cpp

@@ -536,7 +536,7 @@ TEST_F(SourceBlocksDedupTest, source_blocks_chain) {
    succs: (goto B6)\n\
  Block B6:\n\
    preds: (goto B3) (goto B4) (goto B5)\n\
-   SOURCE-BLOCKS: Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I@4294967295() Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I@100() "
+   SOURCE-BLOCKS: Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I@100() "
       "Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I@100() Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I@100()\n\
    POSITION: Lcom/facebook/redextest/SourceBlocksDedupTest;.useSwitch:()I(SourceBlocksDedupTest.java:22)\n\
    OPCODE: INVOKE_VIRTUAL v4, Lcom/facebook/redextest/SourceBlocksDedupTest;.someFunc:()V\n\