Handle REG_SEQUENCE with implicitly defined operands.

Code like that would only be produced by bugpoint, but we should still
handle it correctly.

When a register is defined by a REG_SEQUENCE of undefs, the register
itself is undef. Previously, we would create a register with uses but no
defs.

Fixes part of PR10520.

llvm-svn: 136401

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/ProcessImplicitDefs.cpp b/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
index c04d65637c9..b1d8c976022 100644
--- a/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
+++ b/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
@@ -125,8 +125,14 @@ bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
             LiveVariables::VarInfo& vi = LV->getVarInfo(MO.getReg());
             vi.removeKill(MI);
           }
+          unsigned Reg = MI->getOperand(0).getReg();
           MI->eraseFromParent();
           Changed = true;
+
+          // A REG_SEQUENCE may have been expanded into partial definitions.
+          // If this was the last one, mark Reg as implicitly defined.
+          if (TargetRegisterInfo::isVirtualRegister(Reg) && MRI->def_empty(Reg))
+            ImpDefRegs.insert(Reg);
           continue;
         }
       }