[DebugInfo][InstrRef] Prefer stack locations for variables

This patch adjusts what location is picked for a known variable value --
preferring to leave locations on the stack, even when a value is re-loaded
into a register. The benefit is reduced location list entropy, on a
clang-3.4 build I found that .debug_loclists reduces in size by 6%, from
29Mb down to 27Mb.

Testing: a few tests need the stack slot to be written to explicitly, to
force LiveDebugValues into restoring the variable location to a register.
I've added an explicit test for the desired behaviour in
livedebugvalues_recover_clobbers.mir .

Differential Revision: https://reviews.llvm.org/D120732

1 files changed, 0 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
index 1c0e5ac..74f6e6e8 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -1634,11 +1634,6 @@ bool InstrRefBasedLDV::transferSpillOrRestoreInst(MachineInstr &MI) {
       LocIdx SrcIdx = MTracker->getSpillMLoc(SpillID);
       auto ReadValue = MTracker->readMLoc(SrcIdx);
       MTracker->setReg(DestReg, ReadValue);
-
-      if (TTracker) {
-        LocIdx DstLoc = MTracker->getRegMLoc(DestReg);
-        TTracker->transferMlocs(SrcIdx, DstLoc, MI.getIterator());
-      }
     };
 
     for (MCSubRegIterator SRI(Reg, TRI, false); SRI.isValid(); ++SRI) {