Remove an assertion to fix PR9872.

It can happen that a live debug variable is the last use of a sub-register, and
the register allocator will pick a larger register class for the virtual
register.  If the allocated register doesn't support the sub-register index,
just use %noreg for the debug variables instead of asserting.

In PR9872, a debug variable ends up in the sub_8bit_hi part of a GR32_ABCD
register. The register is split and one part is inflated to GR32 and assigned
%ESI because there are no more normal uses of sub_8bit_hi.

Since %ESI doesn't have that sub-register, substPhysReg asserted. Now it will
simply insert a %noreg instead, and the debug variable will be marked
unavailable in that range.

We don't currently have a way of saying: !"value" is in bits 8-15 of %ESI, I
don't know if DWARF even supports that.

llvm-svn: 131073

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 71df6f8..6ab262d 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -125,7 +125,8 @@ void MachineOperand::substPhysReg(unsigned Reg, const TargetRegisterInfo &TRI) {
   assert(TargetRegisterInfo::isPhysicalRegister(Reg));
   if (getSubReg()) {
     Reg = TRI.getSubReg(Reg, getSubReg());
-    assert(Reg && "Invalid SubReg for physical register");
+    // Note that getSubReg() may return 0 if the sub-register doesn't exist.
+    // That won't happen in legal code.
     setSubReg(0);
   }
   setReg(Reg);