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, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 783a7e1..292928f 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -840,6 +840,9 @@ UserValue::rewriteLocations(VirtRegMap &VRM, const TargetRegisterInfo &TRI) {
     unsigned VirtReg = Loc.getReg();
     if (VRM.isAssignedReg(VirtReg) &&
         TargetRegisterInfo::isPhysicalRegister(VRM.getPhys(VirtReg))) {
+      // This can create a %noreg operand in rare cases when the sub-register
+      // index is no longer available. That means the user value is in a
+      // non-existent sub-register, and %noreg is exactly what we want.
       Loc.substPhysReg(VRM.getPhys(VirtReg), TRI);
     } else if (VRM.getStackSlot(VirtReg) != VirtRegMap::NO_STACK_SLOT &&
                VRM.isSpillSlotUsed(VRM.getStackSlot(VirtReg))) {
@@ -942,6 +945,7 @@ void LDVImpl::emitDebugValues(VirtRegMap *VRM) {
   DEBUG(dbgs() << "********** EMITTING LIVE DEBUG VARIABLES **********\n");
   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
   for (unsigned i = 0, e = userValues.size(); i != e; ++i) {
+    DEBUG(userValues[i]->print(dbgs(), &MF->getTarget()));
     userValues[i]->rewriteLocations(*VRM, *TRI);
     userValues[i]->emitDebugValues(VRM, *LIS, *TII);
   }