Home | History | Annotate | Download | only in arm 
      1 /*
      2  * Copyright (C) 2009 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include "Dalvik.h"
     18 #include "vm/compiler/CompilerInternals.h"
     19 #include "ArmLIR.h"
     20 
     21 /*
     22  * Identify unconditional branches that jump to the immediate successor of the
     23  * branch itself.
     24  */
     25 static void applyRedundantBranchElimination(CompilationUnit *cUnit)
     26 {
     27     ArmLIR *thisLIR;
     28 
     29     for (thisLIR = (ArmLIR *) cUnit->firstLIRInsn;
     30          thisLIR != (ArmLIR *) cUnit->lastLIRInsn;
     31          thisLIR = NEXT_LIR(thisLIR)) {
     32 
     33         /* Branch to the next instruction */
     34         if (thisLIR->opcode == kThumbBUncond) {
     35             ArmLIR *nextLIR = thisLIR;
     36 
     37             while (true) {
     38                 nextLIR = NEXT_LIR(nextLIR);
     39 
     40                 /*
     41                  * Is the branch target the next instruction?
     42                  */
     43                 if (nextLIR == (ArmLIR *) thisLIR->generic.target) {
     44                     thisLIR->flags.isNop = true;
     45                     break;
     46                 }
     47 
     48                 /*
     49                  * Found real useful stuff between the branch and the target.
     50                  * Need to explicitly check the lastLIRInsn here since with
     51                  * method-based JIT the branch might be the last real
     52                  * instruction.
     53                  */
     54                 if (!isPseudoOpcode(nextLIR->opcode) ||
     55                     (nextLIR = (ArmLIR *) cUnit->lastLIRInsn))
     56                     break;
     57             }
     58         }
     59     }
     60 }
     61 
     62 void dvmCompilerApplyGlobalOptimizations(CompilationUnit *cUnit)
     63 {
     64     applyRedundantBranchElimination(cUnit);
     65 }
     66