[LiveDebugValues][InstrRef][1/2] Recover more clobbered variable locations

In various circumstances, when we clobber a register there may be
alternative locations that the value is live in. The classic example would
be a value loaded from the stack, and then clobbered: the value is still
available on the stack. InstrRefBasedLDV was coping with this at block
starts where it's forced to pick a location, however it wasn't searching
for alternative locations when values were clobbered.

This patch notifies the "Transfer Tracker" object when clobbers occur, and
it's able to find alternatives and issue DBG_VALUEs for that location. See:
the added test.

Differential Revision: https://reviews.llvm.org/D88405

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
index 770c46e..38e803d 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
@@ -14,6 +14,7 @@
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetMachine.h"
 
 /// \file LiveDebugValues.cpp
@@ -33,6 +34,12 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+    ForceInstrRefLDV("force-instr-ref-livedebugvalues", cl::Hidden,
+                     cl::desc("Use instruction-ref based LiveDebugValues with "
+                              "normal DBG_VALUE inputs"),
+                     cl::init(false));
+
 /// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
 /// InstrRefBasedLDV to perform location propagation, via the LDVImpl
 /// base class.
@@ -87,6 +94,9 @@ bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
       InstrRefBased = TM.Options.ValueTrackingVariableLocations;
     }
 
+    // Allow the user to force selection of InstrRef LDV.
+    InstrRefBased |= ForceInstrRefLDV;
+
     if (InstrRefBased)
       TheImpl = llvm::makeInstrRefBasedLiveDebugValues();
     else