If all sources of a PHI node are defined by an implicit_def, just emit an implicit_def instead of a copy.

llvm-svn: 50927

Author: Evan Cheng

llvm/lib/CodeGen/PHIElimination.cpp

@@ -127,11 +127,15 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
   return true;
 }
 
-static bool isSourceDefinedByImplicitDef(MachineInstr *MPhi, unsigned SrcIdx,
+static bool isSourceDefinedByImplicitDef(MachineInstr *MPhi,
                                          MachineRegisterInfo  *MRI) {
-  unsigned SrcReg = MPhi->getOperand(SrcIdx*2+1).getReg();
-  MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
-  return DefMI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF;
+  for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) {
+    unsigned SrcReg = MPhi->getOperand(i).getReg();
+    MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
+    if (!DefMI || DefMI->getOpcode() != TargetInstrInfo::IMPLICIT_DEF)
+      return false;
+  }
+  return true;
 }
 
 /// LowerAtomicPHINode - Lower the PHI node at the top of the specified block,
@@ -156,9 +160,9 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB,
   // into the phi node destination.
   //
   const TargetInstrInfo *TII = MF.getTarget().getInstrInfo();
-  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.
+  if (isSourceDefinedByImplicitDef(MPhi, MRI))
+    // If all sources of a PHI node are 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);

llvm/test/CodeGen/X86/2008-05-09-PHIElimBug.ll

@@ -0,0 +1,25 @@
+; RUN: llvm-as < %s | llc -march=x86
+
+	%struct.V = type { <4 x float>, <4 x float>, <4 x float>, <4 x float>, <4 x float>, <4 x float>, <4 x float>, <4 x i32>, float*, float*, float*, float*, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, i32, i32, i32, i32, i32, i32, i32, i32 }
+
+define fastcc void @t() nounwind  {
+entry:
+	br i1 false, label %bb23816.preheader, label %bb23821
+
+bb23816.preheader:		; preds = %entry
+	%tmp23735 = and i32 0, 2		; <i32> [#uses=0]
+	br label %bb23830
+
+bb23821:		; preds = %entry
+	br i1 false, label %bb23830, label %bb23827
+
+bb23827:		; preds = %bb23821
+	%tmp23829 = getelementptr %struct.V* null, i32 0, i32 42		; <i32*> [#uses=0]
+	br label %bb23830
+
+bb23830:		; preds = %bb23827, %bb23821, %bb23816.preheader
+	%scaledInDst.2.reg2mem.5 = phi i8 [ undef, %bb23827 ], [ undef, %bb23821 ], [ undef, %bb23816.preheader ]		; <i8> [#uses=1]
+	%toBool35047 = icmp eq i8 %scaledInDst.2.reg2mem.5, 0		; <i1> [#uses=1]
+	%bothcond39107 = or i1 %toBool35047, false		; <i1> [#uses=0]
+	unreachable
+}