Record CodeGen optimization level in the BranchFolding pass so that we can

use it to control tail merging when there is a tradeoff between performance
and code size.  When there is only 1 instruction in the common tail, we have
been merging.  That can be good for code size but is a definite loss for
performance.  Now we will avoid tail merging in that case when the
optimization level is "Aggressive", i.e., "-O3".  Radar 7338114.

Since the IfConversion pass invokes BranchFolding, it too needs to know
the optimization level.  Note that I removed the RegisterPass instantiation
for IfConversion because it required a default constructor.  If someone
wants to keep that for some reason, we can add a default constructor with
a hard-wired optimization level.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85346 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LLVMTargetMachine.cpp

@@ -329,7 +329,7 @@ bool LLVMTargetMachine::addCommonCodeGenPasses(PassManagerBase &PM,
 
   // Branch folding must be run after regalloc and prolog/epilog insertion.
   if (OptLevel != CodeGenOpt::None) {
-    PM.add(createBranchFoldingPass(getEnableTailMergeDefault()));
+    PM.add(createBranchFoldingPass(getEnableTailMergeDefault(), OptLevel));
     printAndVerify(PM);
   }