1 //===-- PeepholeOpts.cpp --------------------------------------------------===//
3 // Support for performing several peephole opts in one or a few passes over the
4 // machine code of a method.
6 //===----------------------------------------------------------------------===//
8 #include "llvm/CodeGen/PeepholeOpts.h"
9 #include "llvm/CodeGen/MachineBasicBlock.h"
10 #include "llvm/CodeGen/MachineInstr.h"
11 #include "llvm/Target/TargetMachine.h"
12 #include "llvm/Target/MachineInstrInfo.h"
13 #include "llvm/Target/MachineOptInfo.h"
14 #include "llvm/BasicBlock.h"
15 #include "llvm/Pass.h"
17 //************************* Internal Functions *****************************/
20 DeleteInstruction(MachineBasicBlock& mvec,
21 MachineBasicBlock::iterator& BBI,
22 const TargetMachine& target)
24 // Check if this instruction is in a delay slot of its predecessor.
25 if (BBI != mvec.begin())
27 const MachineInstrInfo& mii = target.getInstrInfo();
28 MachineInstr* predMI = *(BBI-1);
29 if (unsigned ndelay = mii.getNumDelaySlots(predMI->getOpCode()))
31 // This instruction is in a delay slot of its predecessor, so
32 // replace it with a nop. By replacing in place, we save having
33 // to update the I-I maps.
35 assert(ndelay == 1 && "Not yet handling multiple-delay-slot targets");
36 (*BBI)->replace(mii.getNOPOpCode(), 0);
41 // The instruction is not in a delay slot, so we can simply erase it.
46 //******************* Individual Peephole Optimizations ********************/
50 RemoveUselessCopies(MachineBasicBlock& mvec,
51 MachineBasicBlock::iterator& BBI,
52 const TargetMachine& target)
54 if (target.getOptInfo().IsUselessCopy(*BBI))
56 DeleteInstruction(mvec, BBI, target);
63 //************************ Class Implementations **************************/
65 class PeepholeOpts: public BasicBlockPass {
66 const TargetMachine ⌖
67 bool visit(MachineBasicBlock& mvec,
68 MachineBasicBlock::iterator BBI) const;
70 PeepholeOpts(const TargetMachine &T): target(T) { }
71 bool runOnBasicBlock(BasicBlock &BB); // apply this pass to each BB
75 // Register the pass with llc only, and not opt...
76 static RegisterLLC<PeepholeOpts>
77 X("peephole", "Peephole Optimization", createPeepholeOptsPass);
80 /* Apply a list of peephole optimizations to this machine instruction
81 * within its local context. They are allowed to delete MI or any
82 * instruction before MI, but not
85 PeepholeOpts::visit(MachineBasicBlock& mvec,
86 MachineBasicBlock::iterator BBI) const
90 /* Remove redundant copy instructions */
91 changed |= RemoveUselessCopies(mvec, BBI, target);
92 if (BBI == mvec.end()) // nothing more to do!
100 PeepholeOpts::runOnBasicBlock(BasicBlock &BB)
102 // Get the machine instructions for this BB
103 MachineBasicBlock& mvec = MachineBasicBlock::get(&BB);
105 // Iterate over all machine instructions in the BB
106 // Use a reverse iterator to allow deletion of MI or any instruction after it.
107 // Insertions or deletions *before* MI are not safe.
109 for (MachineBasicBlock::reverse_iterator RI=mvec.rbegin(),
110 RE=mvec.rend(); RI != RE; )
112 MachineBasicBlock::iterator BBI = RI.base()-1; // save before incr
113 ++RI; // pre-increment to delete MI or after it
121 //===----------------------------------------------------------------------===//
122 // createPeepholeOptsPass - Public entrypoint for peephole optimization
123 // and this file as a whole...
126 createPeepholeOptsPass(TargetMachine &T)
128 return new PeepholeOpts(T);