Debug Info: Simplify Frame Index handling in DBG_VALUE Machine Instructions

Rather than using the full power of target-specific addressing modes in
DBG_VALUEs with Frame Indicies, simply use Frame Index + Offset. This
reduces the complexity of debug info handling down to two
representations of values (reg+offset and frame index+offset) rather
than three or four.

Ideally we could ensure that frame indicies had been eliminated by the
time we reached an assembly or dwarf generation, but I haven't spent the
time to figure out where the FIs are leaking through into that & whether
there's a good place to convert them. Some FI+offset=>reg+offset
conversion is done (see PrologEpilogInserter, for example) which is
necessary for some SelectionDAG assumptions about registers, I believe,
but it might be possible to make this a more thorough conversion &
ensure there are no remaining FIs no matter how instruction selection
is performed.

llvm-svn: 184066

1 files changed, 1 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index 7c03055808d..f8ecc605f17 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -702,12 +702,7 @@ ARMBaseRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   }
 #endif // NDEBUG
 
-  // Special handling of dbg_value instructions.
-  if (MI.isDebugValue()) {
-    MI.getOperand(FIOperandNum).  ChangeToRegister(FrameReg, false /*isDef*/);
-    MI.getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
-    return;
-  }
+  assert(!MI.isDebugValue() && "DBG_VALUEs should be handled in target-independent code");
 
   // Modify MI as necessary to handle as much of 'Offset' as possible
   bool Done = false;