Blockinstrument handle entry block throw

Summary: The IR type checker and quality metrics pipelines broke due to BlockInstrument. If the block to be instrumented throws, do not make the new entry block with the instrument load params throw too.

Reviewed By: agampe

Differential Revision: D54691052

fbshipit-source-id: 63c6cdd716dfe728fb5d4e2a2b9897cfbf1e85c5

opt/instrument/BlockInstrument.cpp

@@ -620,6 +620,13 @@ auto insert_prologue_insts(cfg::ControlFlowGraph& cfg,
     auto it = cfg.find_insn(eb_insn);
     b.block = it.block();
     b.it = it.unwrap();
+    // the entry block with prologue opcodes should not retain throws from the
+    // block that it was split from
+    if (!cfg.entry_block()->cannot_throw()) {
+      cfg.delete_succ_edge_if(cfg.entry_block(), [](const cfg::Edge* e) {
+        return e->type() == cfg::EdgeType::EDGE_THROW;
+      });
+    }
   }
 
   if (slow_invariants_debug) {