[PATCH] fix a leak in CodeGenFunction::EmitSwitchStmt (detected by lsan)

[Kostya Serebryany]

Hi nicholas,

On code like switch (0) { case 0:; } clang leaks one basic block.

First, CodeGenFunction::EmitSwitchStmt creates a new BasicBlock,
then it does the following and exits:
  // See if we can constant fold the condition of the switch and therefore only
  // emit the live case statement (if any) of the switch.
This BasicBlock remains unattached to anything an leaks.

The following fix removes the leak.
Confirmed by running clang on a function with 500K such statements:
the memory footprint drops from 800K to 500K.
(also tested by "check-clang")

Alternative fix may be to move the creation of SwitchExit to some later point,
by my attempts to do so failed (the test CodeGenCXX/condition.cpp starts failing).

http://llvm-reviews.chandlerc.com/D2472

Files:
  lib/CodeGen/CGStmt.cpp

Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp
+++ lib/CodeGen/CGStmt.cpp
@@ -1270,6 +1270,7 @@
       // switches continue to function properly
       SwitchInsn = SavedSwitchInsn;
 
+      delete SwitchExit.getBlock();  // SwitchExit will not be needed.
       return;
     }
   }
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