[GlobalISel] Fix insertion point of new instructions to be after PHIs.

For some reason we sometimes insert new instructions one instruction before
the first non-PHI when legalizing. This can result in having non-PHI
instructions before PHIs, which mean that PHI elimination doesn't catch them.

Differential Revision: https://reviews.llvm.org/D67570

llvm-svn: 371901

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 9239576c994..8c356c62a17 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -931,7 +931,7 @@ LegalizerHelper::LegalizeResult LegalizerHelper::narrowScalar(MachineInstr &MI,
       for (unsigned j = 1; j < MI.getNumOperands(); j += 2)
         MIB.addUse(SrcRegs[j / 2][i]).add(MI.getOperand(j + 1));
     }
-    MIRBuilder.setInsertPt(MBB, --MBB.getFirstNonPHI());
+    MIRBuilder.setInsertPt(MBB, MBB.getFirstNonPHI());
     MIRBuilder.buildMerge(MI.getOperand(0).getReg(), DstRegs);
     Observer.changedInstr(MI);
     MI.eraseFromParent();
@@ -1765,7 +1765,7 @@ LegalizerHelper::widenScalar(MachineInstr &MI, unsigned TypeIdx, LLT WideTy) {
     }
 
     MachineBasicBlock &MBB = *MI.getParent();
-    MIRBuilder.setInsertPt(MBB, --MBB.getFirstNonPHI());
+    MIRBuilder.setInsertPt(MBB, MBB.getFirstNonPHI());
     widenScalarDst(MI, WideTy);
     Observer.changedInstr(MI);
     return Legalized;
@@ -3156,7 +3156,7 @@ LegalizerHelper::moreElementsVectorPhi(MachineInstr &MI, unsigned TypeIdx,
   }
 
   MachineBasicBlock &MBB = *MI.getParent();
-  MIRBuilder.setInsertPt(MBB, --MBB.getFirstNonPHI());
+  MIRBuilder.setInsertPt(MBB, MBB.getFirstNonPHI());
   moreElementsVectorDst(MI, MoreTy, 0);
   Observer.changedInstr(MI);
   return Legalized;