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Teach machine cse to commute instructions.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121903 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2010-12-15 22:16:21 +00:00
parent 0406356cd4
commit a63cde26ff
2 changed files with 59 additions and 2 deletions
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21
lib/CodeGen/MachineCSE.cpp
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@ -24,7 +24,6 @@
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
@ -33,6 +32,7 @@ STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression eliminated");
STATISTIC(NumPhysCSEs,
"Number of physreg referencing common subexpr eliminated");
STATISTIC(NumCommutes, "Number of copies coalesced after commuting");
namespace {
class MachineCSE : public MachineFunctionPass {
@ -368,7 +368,22 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
FoundCSE = VNT.count(MI);
}
}
// FIXME: commute commutable instructions?
// Commute commutable instructions.
bool Commuted = false;
if (!FoundCSE && MI->getDesc().isCommutable()) {
MachineInstr *NewMI = TII->commuteInstruction(MI);
if (NewMI) {
Commuted = true;
FoundCSE = VNT.count(NewMI);
if (NewMI != MI)
// New instruction. It doesn't need to be kept.
NewMI->eraseFromParent();
else if (!FoundCSE)
// MI was changed but it didn't help, commute it back!
(void)TII->commuteInstruction(MI);
}
}
// If the instruction defines physical registers and the values *may* be
// used, then it's not safe to replace it with a common subexpression.
@ -430,6 +445,8 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
++NumCSEs;
if (!PhysRefs.empty())
++NumPhysCSEs;
if (Commuted)
++NumCommutes;
} else {
DEBUG(dbgs() << "*** Not profitable, avoid CSE!\n");
VNT.insert(MI, CurrVN++);