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

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/CodeGen/BranchFolding.h b/lib/CodeGen/BranchFolding.h
index 9763e3339a..5d355256d1 100644
--- a/lib/CodeGen/BranchFolding.h
+++ b/lib/CodeGen/BranchFolding.h
@@ -12,6 +12,7 @@
 
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Target/TargetMachine.h"
 #include <vector>
 
 namespace llvm {
@@ -23,7 +24,7 @@ namespace llvm {
 
   class BranchFolder {
   public:
-    explicit BranchFolder(bool defaultEnableTailMerge);
+    explicit BranchFolder(bool defaultEnableTailMerge, CodeGenOpt::Level OL);
 
     bool OptimizeFunction(MachineFunction &MF,
                           const TargetInstrInfo *tii,
@@ -37,6 +38,7 @@ namespace llvm {
     typedef std::pair<MPIterator, MachineBasicBlock::iterator> SameTailElt;
     std::vector<SameTailElt> SameTails;
 
+    CodeGenOpt::Level OptLevel;
     bool EnableTailMerge;
     const TargetInstrInfo *TII;
     const TargetRegisterInfo *TRI;
@@ -73,8 +75,10 @@ namespace llvm {
                            public BranchFolder {
   public:
     static char ID;
-    explicit BranchFolderPass(bool defaultEnableTailMerge)
-      :  MachineFunctionPass(&ID), BranchFolder(defaultEnableTailMerge) {}
+    explicit BranchFolderPass(bool defaultEnableTailMerge,
+                              CodeGenOpt::Level OptLevel)
+      :  MachineFunctionPass(&ID),
+      BranchFolder(defaultEnableTailMerge, OptLevel) {}
 
     virtual bool runOnMachineFunction(MachineFunction &MF);
     virtual const char *getPassName() const { return "Control Flow Optimizer"; }