Fold predicable instructions into MOVCC / t2MOVCC.

The ARM select instructions are just predicated moves. If the select is
the only use of an operand, the instruction defining the operand can be
predicated instead, saving one instruction and decreasing register
pressure.

This implementation can turn AND/ORR/EOR instructions into their
corresponding ANDCC/ORRCC/EORCC variants. Ideally, we should be able to
predicate any instruction, but we don't yet support predicated
instructions in SSA form.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161994 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 057fd71..aa45253 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1568,6 +1568,55 @@ ARMBaseInstrInfo::commuteInstruction(MachineInstr *MI, bool NewMI) const {
   return TargetInstrInfoImpl::commuteInstruction(MI, NewMI);
 }
 
+/// Identify instructions that can be folded into a MOVCC instruction, and
+/// return the corresponding opcode for the predicated pseudo-instruction.
+unsigned llvm::canFoldARMInstrIntoMOVCC(unsigned Reg,
+                                        MachineInstr *&MI,
+                                        const MachineRegisterInfo &MRI) {
+  if (!TargetRegisterInfo::isVirtualRegister(Reg))
+    return 0;
+  if (!MRI.hasOneNonDBGUse(Reg))
+    return 0;
+  MI = MRI.getVRegDef(Reg);
+  if (!MI)
+    return 0;
+  // Check if MI has any non-dead defs or physreg uses. This also detects
+  // predicated instructions which will be reading CPSR.
+  for (unsigned i = 1, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg())
+      continue;
+    if (TargetRegisterInfo::isPhysicalRegister(MO.getReg()))
+      return 0;
+    if (MO.isDef() && !MO.isDead())
+      return 0;
+  }
+  switch (MI->getOpcode()) {
+  default: return 0;
+  case ARM::ANDri:   return ARM::ANDCCri;
+  case ARM::ANDrr:   return ARM::ANDCCrr;
+  case ARM::ANDrsi:  return ARM::ANDCCrsi;
+  case ARM::ANDrsr:  return ARM::ANDCCrsr;
+  case ARM::t2ANDri: return ARM::t2ANDCCri;
+  case ARM::t2ANDrr: return ARM::t2ANDCCrr;
+  case ARM::t2ANDrs: return ARM::t2ANDCCrs;
+  case ARM::EORri:   return ARM::EORCCri;
+  case ARM::EORrr:   return ARM::EORCCrr;
+  case ARM::EORrsi:  return ARM::EORCCrsi;
+  case ARM::EORrsr:  return ARM::EORCCrsr;
+  case ARM::t2EORri: return ARM::t2EORCCri;
+  case ARM::t2EORrr: return ARM::t2EORCCrr;
+  case ARM::t2EORrs: return ARM::t2EORCCrs;
+  case ARM::ORRri:   return ARM::ORRCCri;
+  case ARM::ORRrr:   return ARM::ORRCCrr;
+  case ARM::ORRrsi:  return ARM::ORRCCrsi;
+  case ARM::ORRrsr:  return ARM::ORRCCrsr;
+  case ARM::t2ORRri: return ARM::t2ORRCCri;
+  case ARM::t2ORRrr: return ARM::t2ORRCCrr;
+  case ARM::t2ORRrs: return ARM::t2ORRCCrs;
+  }
+}
+
 /// Map pseudo instructions that imply an 'S' bit onto real opcodes. Whether the
 /// instruction is encoded with an 'S' bit is determined by the optional CPSR
 /// def operand.