Subzero: Add branch optimization.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the TargetLoweringX8632 class, which
@@ skipping 381 matching lines @@
   Func->genFrame();
   if (Func->hasError())
     return;
   T_genFrame.printElapsedUs(Context, "genFrame()");
   Func->dump("After stack frame mapping");
 
   // Nop insertion
   if (shouldDoNopInsertion()) {
     Func->doNopInsertion();
   }
+
+  // Branch optimization.  This needs to be done just before code

[jvoung (off chromium), 2014/09/18 03:56:02]

Should this be before nop insertion? I don't think that will reorder or insert
CfgNodes, but if before then you will at least not need to iterate over the nops
to find the branches.

[Jim Stichnoth, 2014/09/18 11:45:51]

Good point, done.

+  // emission.  In particular, no transformations that insert or
+  // reorder CfgNodes should be done after branch optimization.
+  Func->doBranchOpt();
+  Func->dump("After branch optimization");
 }
 
 void TargetX8632::translateOm1() {
   GlobalContext *Context = Func->getContext();
   Timer T_placePhiLoads;
   Func->placePhiLoads();
   if (Func->hasError())
     return;
   T_placePhiLoads.printElapsedUs(Context, "placePhiLoads()");
   Timer T_placePhiStores;
@@ skipping 25 matching lines @@
     return;
   T_genFrame.printElapsedUs(Context, "genFrame()");
   Func->dump("After stack frame mapping");
 
   // Nop insertion
   if (shouldDoNopInsertion()) {
     Func->doNopInsertion();
   }
 }
 
+void TargetX8632::doBranchOpt(Inst *I, const CfgNode *NextNode) {
+  if (InstX8632Br *Br = llvm::dyn_cast<InstX8632Br>(I)) {
+    Br->optimizeBranch(NextNode);
+  }
+}
+
 IceString TargetX8632::RegNames[] = {
 #define X(val, init, name, name16, name8, scratch, preserved, stackptr,        \
           frameptr, isI8, isInt, isFP)                                         \
   name,
   REGX8632_TABLE
 #undef X
 };
 
 Variable *TargetX8632::getPhysicalRegister(SizeT RegNum) {
   assert(RegNum < PhysicalRegisters.size());
@@ skipping 4077 matching lines @@
     Str << "\t.align\t" << Align << "\n";
     Str << MangledName << ":\n";
     for (SizeT i = 0; i < Size; ++i) {
       Str << "\t.byte\t" << (((unsigned)Data[i]) & 0xff) << "\n";
     }
     Str << "\t.size\t" << MangledName << ", " << Size << "\n";
   }
 }
 
 } // end of namespace Ice