Re-enable improvements to debug emission for optimized code

Reverts dotnet#33021, which was a reversion of dotnet#2107.

Fix the IG boundary sensitivity for debug emission.

Allow debug info to be summarized in a way that makes it amenable to analyze
with our jitutils tooling (namely, `jit-analyze`).

Author: AndyAyersMS

src/coreclr/src/jit/codegencommon.cpp

@@ -12314,9 +12314,28 @@ 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())
@@ -12707,7 +12726,7 @@ void CodeGenInterface::VariableLiveKeeper::siEndAllVariableLiveRange(VARSET_VALA
 // Notes:
 //    This overload exists for the case we are jitting code compiled in
 //    debug mode. When that happen we don't have variable liveness info
-//    as "BaiscBlock::bbLiveIn" or "BaiscBlock::bbLiveOut" and there is no
+//    as "BasicBlock::bbLiveIn" or "BasicBlock::bbLiveOut" and there is no
 //    tracked variable.
 //
 void CodeGenInterface::VariableLiveKeeper::siEndAllVariableLiveRange()

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/ee_il_dll.cpp

@@ -835,8 +835,21 @@ void Compiler::eeDispVar(ICorDebugInfo::NativeVarInfo* var)
 // Same parameters as ICorStaticInfo::setVars().
 void Compiler::eeDispVars(CORINFO_METHOD_HANDLE ftn, ULONG32 cVars, ICorDebugInfo::NativeVarInfo* vars)
 {
-    printf("*************** Variable debug info\n");
-    printf("%d live ranges\n", cVars);
+    // Estimate number of unique vars with debug info
+    //
+    ALLVARSET_TP uniqueVars(AllVarSetOps::MakeEmpty(this));
+    for (unsigned i = 0; i < cVars; i++)
+    {
+        // ignore "special vars" and out of bounds vars
+        if ((((int)vars[i].varNumber) >= 0) && (vars[i].varNumber < lclMAX_ALLSET_TRACKED))
+        {
+            AllVarSetOps::AddElemD(this, uniqueVars, vars[i].varNumber);
+        }
+    }
+
+    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++)
     {
         eeDispVar(&vars[i]);

src/coreclr/src/jit/emit.cpp

@@ -65,6 +65,33 @@ 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, or the first instruction of
+//  an extension of this location's IG.
+//
+// Arguments:
+//  emit - an emitter* instance
+//
+bool emitLocation::IsPreviousInsNum(const 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/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(LONG compMethodID) const;
 #endif // DEBUG
@@ -2386,7 +2388,7 @@ 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);