Change debug info default variable tracking system

src/coreclr/src/jit/codegenarmarch.cpp

@@ -2412,11 +2412,11 @@ void CodeGen::genRegCopy(GenTree* treeNode)
 
 #ifdef USING_VARIABLE_LIVE_RANGE
                 // Report the home change for this variable
-                varLiveKeeper->siUpdateVariableLiveRange(varDsc, lcl->GetLclNum())
+                varLiveKeeper->siUpdateVariableLiveRange(varDsc, lcl->GetLclNum());
 #endif // USING_VARIABLE_LIVE_RANGE
 
-                    // The new location is going live
-                    genUpdateRegLife(varDsc, /*isBorn*/ true, /*isDying*/ false DEBUGARG(treeNode));
+                // The new location is going live
+                genUpdateRegLife(varDsc, /*isBorn*/ true, /*isDying*/ false DEBUGARG(treeNode));
             }
         }
     }

src/coreclr/src/jit/codegencommon.cpp

@@ -11466,9 +11466,19 @@ 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() && m_VariableLiveRanges->back().m_EndEmitLocation.IsPreviousInsNum(emit) &&
+        siVarLoc::Equals(&varLocation, &(m_VariableLiveRanges->back().m_VarLocation)))
+    {
+        // 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
+    {
+        // 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/src/jit/codegeninterface.h

@@ -26,11 +26,11 @@
 #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/src/jit/emit.cpp

@@ -65,6 +65,21 @@ 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(const emitter* emit) const
+{
+    assert(Valid());
+    bool isSameGroup  = (ig == emit->emitCurIG);
+    bool isSameInsNum = (emitGetInsNumFromCodePos(codePos) == emitGetInsNumFromCodePos(emit->emitCurOffset()) - 1);
+    return isSameGroup && isSameInsNum;
+}
+
 #ifdef DEBUG
 void emitLocation::Print() const
 {

src/coreclr/src/jit/emit.h

@@ -191,6 +191,8 @@ class emitLocation
 
     UNATIVE_OFFSET GetFuncletPrologOffset(emitter* emit) const;
 
+    bool emitLocation::IsPreviousInsNum(const emitter* emit) const;
+
 #ifdef DEBUG
     void Print() const;
 #endif // DEBUG
@@ -2389,7 +2391,7 @@ inline unsigned emitGetInsOfsFromCodePos(unsigned codePos)
     return (codePos >> 16);
 }
 
-inline unsigned emitter::emitCurOffset()
+inline unsigned emitter::emitCurOffset() const
 {
     unsigned codePos = emitCurIGinsCnt + (emitCurIGsize << 16);
 

src/coreclr/src/jit/emitpub.h

@@ -65,7 +65,7 @@ void emitFinishPrologEpilogGeneration();
 /************************************************************************/
 
 void*    emitCurBlock();
-unsigned emitCurOffset();
+unsigned emitCurOffset() const;
 
 UNATIVE_OFFSET emitCodeOffset(void* blockPtr, unsigned codeOffs);