Re-enable USING_VARIABLE_LIVE_RANGE

src/coreclr/jit/codegencommon.cpp

@@ -11863,9 +11863,28 @@ void CodeGenInterface::VariableLiveKeeper::VariableLiveDescriptor::startLiveRang
     // Is the first "VariableLiveRange" or the previous one has been closed so its "m_EndEmitLocation" is valid
     noway_assert(m_VariableLiveRanges->empty() || m_VariableLiveRanges->back().m_EndEmitLocation.Valid());
 
-    // Creates new live range with invalid end
-    m_VariableLiveRanges->emplace_back(varLocation, emitLocation(), emitLocation());
-    m_VariableLiveRanges->back().m_StartEmitLocation.CaptureLocation(emit);
+    if (!m_VariableLiveRanges->empty() &&
+        siVarLoc::Equals(&varLocation, &(m_VariableLiveRanges->back().m_VarLocation)) &&
+        m_VariableLiveRanges->back().m_EndEmitLocation.IsPreviousInsNum(emit))
+    {
+        JITDUMP("Extending debug range...\n");
+
+        // The variable is being born just after the instruction at which it died.
+        // In this case, i.e. an update of the variable's value, we coalesce the live ranges.
+        m_VariableLiveRanges->back().m_EndEmitLocation.Init();
+    }
+    else
+    {
+        JITDUMP("New debug range: %s\n",
+                m_VariableLiveRanges->empty()
+                    ? "first"
+                    : siVarLoc::Equals(&varLocation, &(m_VariableLiveRanges->back().m_VarLocation))
+                          ? "new var or location"
+                          : "not adjacent");
+        // Creates new live range with invalid end
+        m_VariableLiveRanges->emplace_back(varLocation, emitLocation(), emitLocation());
+        m_VariableLiveRanges->back().m_StartEmitLocation.CaptureLocation(emit);
+    }
 
 #ifdef DEBUG
     if (!m_VariableLifeBarrier->hasLiveRangesToDump())

src/coreclr/jit/codegeninterface.h

@@ -25,11 +25,11 @@
 #include "treelifeupdater.h"
 #include "emit.h"
 
-#if 1
+#if 0
 // Enable USING_SCOPE_INFO flag to use psiScope/siScope info to report variables' locations.
 #define USING_SCOPE_INFO
 #endif
-#if 0
+#if 1
 // Enable USING_VARIABLE_LIVE_RANGE flag to use VariableLiveRange info to report variables' locations.
 // Note: if both USING_SCOPE_INFO and USING_VARIABLE_LIVE_RANGE are defined, then USING_SCOPE_INFO
 // information is reported to the debugger.

src/coreclr/jit/ee_il_dll.cpp

@@ -861,6 +861,8 @@ void Compiler::eeDispVar(ICorDebugInfo::NativeVarInfo* var)
 // Same parameters as ICorStaticInfo::setVars().
 void Compiler::eeDispVars(CORINFO_METHOD_HANDLE ftn, ULONG32 cVars, ICorDebugInfo::NativeVarInfo* vars)
 {
+    // Estimate number of unique vars with debug info
+    //
     ALLVARSET_TP uniqueVars(AllVarSetOps::MakeEmpty(this));
     for (unsigned i = 0; i < cVars; i++)
     {
@@ -870,7 +872,8 @@ void Compiler::eeDispVars(CORINFO_METHOD_HANDLE ftn, ULONG32 cVars, ICorDebugInf
             AllVarSetOps::AddElemD(this, uniqueVars, vars[i].varNumber);
         }
     }
-    printf("; Variable debug info: %d live range(s), %d var(s) for method %s\n", cVars,
+
+    printf("; Variable debug info: %d live ranges, %d vars for method %s\n", cVars,
            AllVarSetOps::Count(this, uniqueVars), info.compFullName);
 
     for (unsigned i = 0; i < cVars; i++)

src/coreclr/jit/emit.cpp

@@ -64,6 +64,32 @@ UNATIVE_OFFSET emitLocation::GetFuncletPrologOffset(emitter* emit) const
     return emit->emitCurIGsize;
 }
 
+//------------------------------------------------------------------------
+// IsPreviousInsNum: Returns true if the emitter is on the next instruction
+//  of the same group as this emitLocation.
+//
+// Arguments:
+//  emit - an emitter* instance
+//
+bool emitLocation::IsPreviousInsNum(emitter* emit) const
+{
+    assert(Valid());
+
+    // Within the same IG?
+    if (ig == emit->emitCurIG)
+    {
+        return (emitGetInsNumFromCodePos(codePos) == emitGetInsNumFromCodePos(emit->emitCurOffset()) - 1);
+    }
+
+    // Spanning an IG boundary?
+    if (ig->igNext == emit->emitCurIG)
+    {
+        return (emitGetInsNumFromCodePos(codePos) == ig->igInsCnt) && (emit->emitCurIGinsCnt == 1);
+    }
+
+    return false;
+}
+
 #ifdef DEBUG
 void emitLocation::Print(LONG compMethodID) const
 {

src/coreclr/jit/emit.h

@@ -190,6 +190,8 @@ class emitLocation
 
     UNATIVE_OFFSET GetFuncletPrologOffset(emitter* emit) const;
 
+    bool IsPreviousInsNum(emitter* emit) const;
+
 #ifdef DEBUG
     void Print(LONG compMethodID) const;
 #endif // DEBUG