[DebugInfo][InstrRef] Use PHI placement utilities for machine locations

InstrRefBasedLDV used to try and determine which values are in which
registers using a lattice approach; however this is hard to understand, and
broken in various ways. This patch replaces that approach with a standard
SSA approach using existing LLVM utilities. PHIs are placed at dominance
frontiers; value propagation then eliminates un-necessary PHIs.

This patch also adds a bunch of unit tests that should cover many of the
weirder forms of control flow.

Differential Revision: https://reviews.llvm.org/D110173

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
index 43fc17a..214f904 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
@@ -1014,8 +1014,9 @@ private:
   /// had their instruction creation deferred.
   void flushPendingLocs(VarLocInMBB &PendingInLocs, VarLocMap &VarLocIDs);
 
-  bool ExtendRanges(MachineFunction &MF, TargetPassConfig *TPC,
-                    unsigned InputBBLimit, unsigned InputDbgValLimit) override;
+  bool ExtendRanges(MachineFunction &MF, MachineDominatorTree *DomTree,
+                    TargetPassConfig *TPC, unsigned InputBBLimit,
+                    unsigned InputDbgValLimit) override;
 
 public:
   /// Default construct and initialize the pass.
@@ -2107,9 +2108,11 @@ void VarLocBasedLDV::recordEntryValue(const MachineInstr &MI,
 
 /// Calculate the liveness information for the given machine function and
 /// extend ranges across basic blocks.
-bool VarLocBasedLDV::ExtendRanges(MachineFunction &MF, TargetPassConfig *TPC,
-                                  unsigned InputBBLimit,
+bool VarLocBasedLDV::ExtendRanges(MachineFunction &MF,
+                                  MachineDominatorTree *DomTree,
+                                  TargetPassConfig *TPC, unsigned InputBBLimit,
                                   unsigned InputDbgValLimit) {
+  (void)DomTree;
   LLVM_DEBUG(dbgs() << "\nDebug Range Extension\n");
 
   if (!MF.getFunction().getSubprogram())