If a PHI node has a single implicit_def source, replace it with an implicit_def instead of a copy.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49543 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 37b7f45..a82e78e 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/lib/CodeGen/PHIElimination.cpp
@@ -18,6 +18,7 @@
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
@@ -126,6 +127,13 @@
return true;
}
+static bool isSourceDefinedByImplicitDef(MachineInstr *MPhi, unsigned SrcIdx,
+ MachineRegisterInfo *MRI) {
+ unsigned SrcReg = MPhi->getOperand(SrcIdx*2+1).getReg();
+ MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
+ return DefMI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF;
+}
+
/// LowerAtomicPHINode - Lower the PHI node at the top of the specified block,
/// under the assuption that it needs to be lowered in a way that supports
/// atomic execution of PHIs. This lowering method is always correct all of the
@@ -135,6 +143,7 @@
// Unlink the PHI node from the basic block, but don't delete the PHI yet.
MachineInstr *MPhi = MBB.remove(MBB.begin());
+ unsigned NumSrcs = (MPhi->getNumOperands() - 1) / 2;
unsigned DestReg = MPhi->getOperand(0).getReg();
// Create a new register for the incoming PHI arguments.
@@ -147,7 +156,12 @@
// into the phi node destination.
//
const TargetInstrInfo *TII = MF.getTarget().getInstrInfo();
- TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC);
+ if (NumSrcs == 1 && isSourceDefinedByImplicitDef(MPhi, 0, MRI))
+ // If the only source of a PHI node is an implicit_def, just emit an
+ // implicit_def instead of a copy.
+ BuildMI(MBB, AfterPHIsIt, TII->get(TargetInstrInfo::IMPLICIT_DEF), DestReg);
+ else
+ TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC);
// Update live variable information if there is any...
LiveVariables *LV = getAnalysisToUpdate<LiveVariables>();
@@ -189,13 +203,13 @@
// the IncomingReg register in the corresponding predecessor basic block.
//
SmallPtrSet<MachineBasicBlock*, 8> MBBsInsertedInto;
- for (int i = MPhi->getNumOperands() - 1; i >= 2; i-=2) {
- unsigned SrcReg = MPhi->getOperand(i-1).getReg();
+ for (int i = NumSrcs - 1; i >= 0; --i) {
+ unsigned SrcReg = MPhi->getOperand(i*2+1).getReg();
assert(TargetRegisterInfo::isVirtualRegister(SrcReg) &&
"Machine PHI Operands must all be virtual registers!");
// If source is defined by an implicit def, there is no need to insert
- // a copy.
+ // a copy unless it's the only source.
MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
if (DefMI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF) {
ImpDefs.insert(DefMI);
@@ -204,7 +218,7 @@
// Get the MachineBasicBlock equivalent of the BasicBlock that is the
// source path the PHI.
- MachineBasicBlock &opBlock = *MPhi->getOperand(i).getMBB();
+ MachineBasicBlock &opBlock = *MPhi->getOperand(i*2+2).getMBB();
// Check to make sure we haven't already emitted the copy for this block.
// This can happen because PHI nodes may have multiple entries for the