1 //===-- PeepholeOpts.cpp --------------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Support for performing several peephole opts in one or a few passes over the
11 // machine code of a method.
13 //===----------------------------------------------------------------------===//
15 #include "SparcInternals.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineInstr.h"
18 #include "llvm/Target/TargetMachine.h"
19 #include "llvm/Target/TargetInstrInfo.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Pass.h"
23 //************************* Internal Functions *****************************/
26 DeleteInstruction(MachineBasicBlock& mvec,
27 MachineBasicBlock::iterator& BBI,
28 const TargetMachine& target) {
29 // Check if this instruction is in a delay slot of its predecessor.
30 if (BBI != mvec.begin()) {
31 const TargetInstrInfo& mii = target.getInstrInfo();
32 MachineInstr* predMI = *(BBI-1);
33 if (unsigned ndelay = mii.getNumDelaySlots(predMI->getOpCode())) {
34 // This instruction is in a delay slot of its predecessor, so
35 // replace it with a nop. By replacing in place, we save having
36 // to update the I-I maps.
38 assert(ndelay == 1 && "Not yet handling multiple-delay-slot targets");
39 (*BBI)->replace(mii.getNOPOpCode(), 0);
44 // The instruction is not in a delay slot, so we can simply erase it.
49 //******************* Individual Peephole Optimizations ********************/
51 //----------------------------------------------------------------------------
52 // Function: IsUselessCopy
53 // Decide whether a machine instruction is a redundant copy:
54 // -- ADD with g0 and result and operand are identical, or
55 // -- OR with g0 and result and operand are identical, or
56 // -- FMOVS or FMOVD and result and operand are identical.
57 // Other cases are possible but very rare that they would be useless copies,
58 // so it's not worth analyzing them.
59 //----------------------------------------------------------------------------
61 static bool IsUselessCopy(const TargetMachine &target, const MachineInstr* MI) {
62 if (MI->getOpCode() == V9::FMOVS || MI->getOpCode() == V9::FMOVD) {
63 return (/* both operands are allocated to the same register */
64 MI->getOperand(0).getAllocatedRegNum() ==
65 MI->getOperand(1).getAllocatedRegNum());
66 } else if (MI->getOpCode() == V9::ADDr || MI->getOpCode() == V9::ORr) {
67 unsigned srcWithDestReg;
69 for (srcWithDestReg = 0; srcWithDestReg < 2; ++srcWithDestReg)
70 if (MI->getOperand(srcWithDestReg).hasAllocatedReg() &&
71 MI->getOperand(srcWithDestReg).getAllocatedRegNum()
72 == MI->getOperand(2).getAllocatedRegNum())
75 if (srcWithDestReg == 2)
78 /* else source and dest are allocated to the same register */
79 unsigned otherOp = 1 - srcWithDestReg;
80 return (/* either operand otherOp is register %g0 */
81 (MI->getOperand(otherOp).hasAllocatedReg() &&
82 MI->getOperand(otherOp).getAllocatedRegNum() ==
83 target.getRegInfo().getZeroRegNum()) ||
85 /* or operand otherOp == 0 */
86 (MI->getOperand(otherOp).getType()
87 == MachineOperand::MO_SignExtendedImmed &&
88 MI->getOperand(otherOp).getImmedValue() == 0));
96 RemoveUselessCopies(MachineBasicBlock& mvec,
97 MachineBasicBlock::iterator& BBI,
98 const TargetMachine& target) {
99 if (IsUselessCopy(target, *BBI)) {
100 DeleteInstruction(mvec, BBI, target);
107 //************************ Class Implementations **************************/
109 class PeepholeOpts: public BasicBlockPass {
110 const TargetMachine ⌖
111 bool visit(MachineBasicBlock& mvec,
112 MachineBasicBlock::iterator BBI) const;
114 PeepholeOpts(const TargetMachine &T): target(T) { }
115 bool runOnBasicBlock(BasicBlock &BB); // apply this pass to each BB
116 virtual const char *getPassName() const { return "Peephole Optimization"; }
119 // Apply a list of peephole optimizations to this machine instruction
120 // within its local context. They are allowed to delete MI or any
121 // instruction before MI, but not
123 bool PeepholeOpts::visit(MachineBasicBlock& mvec,
124 MachineBasicBlock::iterator BBI) const {
125 /* Remove redundant copy instructions */
126 return RemoveUselessCopies(mvec, BBI, target);
130 bool PeepholeOpts::runOnBasicBlock(BasicBlock &BB) {
131 // Get the machine instructions for this BB
132 // FIXME: MachineBasicBlock::get() is deprecated, hence inlining the function
133 const Function *F = BB.getParent();
134 MachineFunction &MF = MachineFunction::get(F);
135 MachineBasicBlock *MBB = NULL;
136 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
137 if (I->getBasicBlock() == &BB)
140 assert(MBB && "MachineBasicBlock object not found for specified block!");
141 MachineBasicBlock &mvec = *MBB;
143 // Iterate over all machine instructions in the BB
144 // Use a reverse iterator to allow deletion of MI or any instruction after it.
145 // Insertions or deletions *before* MI are not safe.
147 for (MachineBasicBlock::reverse_iterator RI=mvec.rbegin(),
148 RE=mvec.rend(); RI != RE; ) {
149 MachineBasicBlock::iterator BBI = RI.base()-1; // save before incr
150 ++RI; // pre-increment to delete MI or after it
158 //===----------------------------------------------------------------------===//
159 // createPeepholeOptsPass - Public entrypoint for peephole optimization
160 // and this file as a whole...
162 FunctionPass* createPeepholeOptsPass(TargetMachine &T) {
163 return new PeepholeOpts(T);