Avoid reporting empty debug info ranges to the vm (#77289)

* Removing empty variable live ranges

The debugger is not using empty variable live ranges.
We are reporting them because they can get extended
later if the variable becomes alive in the immediately
next emitted instruction. If an empty live range is
not getting extended, which we can realize after
emitting all the code or creating a new live range
for the same variable, we can remove it.

* Extending variable live ranges in more cases

When the emitter moved to the next group but has not
emitted any instruction, and the variable died and
becomes alive again, we would like to extend its range.

* Avoiding creating a new debug range when previous is empty

* Updating check for empty debug ranges

* Updating print

* Avoiding printing twice variable live range

* Avoiding reporting empty variable ranges to the vm

* Revert "Avoiding printing twice variable live range"

This reverts commit 4e1cf47.

* Revert "Updating print"

This reverts commit 7b79b0d.

* Revert "Updating check for empty debug ranges"

This reverts commit e8b102d.

* Revert "Avoiding creating a new debug range when previous is empty"

This reverts commit a11fd5d.

* Revert "Extending variable live ranges in more cases"

This reverts commit 609605a.

* Revert "Removing empty variable live ranges"

This reverts commit 66d18e0.

* Freeing vm memory when there is no debug info

* Persisting JIT-EE contract on empty debug info

* Update src/coreclr/jit/ee_il_dll.cpp

Co-authored-by: Jakob Botsch Nielsen <[email protected]>

Co-authored-by: Brian Bohe <[email protected]>
Co-authored-by: Jakob Botsch Nielsen <[email protected]>

Author: 3 people

src/coreclr/jit/codegencommon.cpp

@@ -6952,8 +6952,11 @@ void CodeGen::genSetScopeInfoUsingVariableRanges()
                 end++;
             }
 
-            genSetScopeInfo(liveRangeIndex, start, end - start, varNum, varNum, true, loc);
-            liveRangeIndex++;
+            if (start < end)
+            {
+                genSetScopeInfo(liveRangeIndex, start, end - start, varNum, varNum, true, loc);
+                liveRangeIndex++;
+            }
         };
 
         siVarLoc*      curLoc   = nullptr;

src/coreclr/jit/ee_il_dll.cpp

@@ -693,9 +693,15 @@ void Compiler::eeSetLVdone()
         eeDispVars(info.compMethodHnd, eeVarsCount, (ICorDebugInfo::NativeVarInfo*)eeVars);
     }
 #endif // DEBUG
+    if ((eeVarsCount == 0) && (eeVars != nullptr))
+    {
+        // We still call setVars with nullptr when eeVarsCount is 0 as part of the contract.
+        // We also need to free the nonused memory.
+        info.compCompHnd->freeArray(eeVars);
+        eeVars = nullptr;
+    }
 
     info.compCompHnd->setVars(info.compMethodHnd, eeVarsCount, (ICorDebugInfo::NativeVarInfo*)eeVars);
-
     eeVars = nullptr; // We give up ownership after setVars()
 }