JIT: fix filter liveness computation

src/jit/liveness.cpp

@@ -1056,6 +1056,42 @@ void Compiler::fgExtendDbgLifetimes()
 #endif // DEBUG
 }
 
+//------------------------------------------------------------------------
+// fgGetHandlerLiveVars: determine set of locals live because of implicit
+//   exception flow from a block.
+//
+// Arguments:
+//    block - the block in question
+//
+// Returns:
+//    Additional set of locals to be considered live throughout the block.
+//
+// Notes:
+//    Assumes caller has screened candidate blocks to only those with
+//    exception flow, via `ehBlockHasExnFlowDsc`.
+//
+//    Exception flow can arise because of a newly raised exception (for
+//    blocks within try regions) or because of an actively propagating exception
+//    (for filter blocks). This flow effectively creates additional successor
+//    edges in the flow graph that the jit does not model. This method computes
+//    the net contribution from all the missing successor edges.
+//
+//    For example, with the following C# source, during EH processing of the throw,
+//    the outer filter will execute in pass1, before the inner handler executes
+//    in pass2, and so the filter blocks should show the inner handler's local is live.
+//
+//    try
+//    {
+//        using (AllocateObject())   // ==> try-finally; handler calls Dispose
+//        {
+//            throw new Exception();
+//        }
+//    }
+//    catch (Exception e1) when (IsExpectedException(e1))
+//    {
+//        Console.WriteLine("In catch 1");
+//    }
+
 VARSET_VALRET_TP Compiler::fgGetHandlerLiveVars(BasicBlock* block)
 {
     noway_assert(block);
@@ -1067,7 +1103,6 @@ VARSET_VALRET_TP Compiler::fgGetHandlerLiveVars(BasicBlock* block)
     do
     {
         /* Either we enter the filter first or the catch/finally */
-
         if (HBtab->HasFilter())
         {
             VarSetOps::UnionD(this, liveVars, HBtab->ebdFilter->bbLiveIn);
@@ -1099,6 +1134,72 @@ VARSET_VALRET_TP Compiler::fgGetHandlerLiveVars(BasicBlock* block)
 
     } while (true);
 
+    // If this block is within a filter, we also need to report as live
+    // any vars live into enclosed finally or fault handlers, since the
+    // filter will run during the first EH pass, and enclosed or enclosing
+    // handlers will run during the second EH pass. So all these handlers
+    // are "exception flow" successors of the filter.
+    //
+    // Note we are relying on ehBlockHasExnFlowDsc to return true
+    // for any filter block that we should examine here.
+    if (block->hasHndIndex())
+    {
+        const unsigned thisHndIndex   = block->getHndIndex();
+        EHblkDsc*      enclosingHBtab = ehGetDsc(thisHndIndex);
+
+        if (enclosingHBtab->InFilterRegionBBRange(block))
+        {
+            assert(enclosingHBtab->HasFilter());
+
+            // Search the EH table for enclosed regions.
+            //
+            // All the enclosed regions will be lower numbered and
+            // immediately prior to and contiguous with the enclosing
+            // region in the EH tab.
+            unsigned index = thisHndIndex;
+
+            while (index > 0)
+            {
+                index--;
+                unsigned enclosingIndex = ehGetEnclosingTryIndex(index);
+                bool     isEnclosed     = false;
+
+                // To verify this is an enclosed region, search up
+                // through the enclosing regions until we find the
+                // region associated with the filter.
+                while (enclosingIndex != EHblkDsc::NO_ENCLOSING_INDEX)
+                {
+                    if (enclosingIndex == thisHndIndex)
+                    {
+                        isEnclosed = true;
+                        break;
+                    }
+
+                    enclosingIndex = ehGetEnclosingTryIndex(enclosingIndex);
+                }
+
+                // If we found an enclosed region, check if the region
+                // is a try fault or try finally, and if so, add any
+                // locals live into the enclosed region's handler into this
+                // block's live-in set.
+                if (isEnclosed)
+                {
+                    EHblkDsc* enclosedHBtab = ehGetDsc(index);
+
+                    if (enclosedHBtab->HasFinallyOrFaultHandler())
+                    {
+                        VarSetOps::UnionD(this, liveVars, enclosedHBtab->ebdHndBeg->bbLiveIn);
+                    }
+                }
+                // Once we run across a non-enclosed region, we can stop searching.
+                else
+                {
+                    break;
+                }
+            }
+        }
+    }
+
     return liveVars;
 }
 
@@ -1171,14 +1272,17 @@ class LiveVarAnalysis
         // since (without proof otherwise) the use and def may touch different memory at run-time.
         m_memoryLiveIn = m_memoryLiveOut | block->bbMemoryUse;
 
-        /* Can exceptions from this block be handled (in this function)? */
-
+        // Does this block have implicit exception flow to a filter or handler?
+        // If so, include the effects of that flow.
         if (m_compiler->ehBlockHasExnFlowDsc(block))
         {
             const VARSET_TP& liveVars(m_compiler->fgGetHandlerLiveVars(block));
-
             VarSetOps::UnionD(m_compiler, m_liveIn, liveVars);
             VarSetOps::UnionD(m_compiler, m_liveOut, liveVars);
+
+            // Implicit eh edges can induce loop-like behavior,
+            // so make sure we iterate to closure.
+            m_hasPossibleBackEdge = true;
         }
 
         /* Has there been any change in either live set? */
@@ -2399,7 +2503,6 @@ void Compiler::fgInterBlockLocalVarLiveness()
         if (block->bbCatchTyp != BBCT_NONE)
         {
             /* Note the set of variables live on entry to exception handler */
-
             VarSetOps::UnionD(this, exceptVars, block->bbLiveIn);
         }
 

tests/src/JIT/Regression/JitBlue/GitHub_22330/GitHub_22330.cs

@@ -1,3 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System;
 using System.Runtime.CompilerServices;
 
@@ -46,4 +50,4 @@ public static int Main()
         Console.WriteLine($"Result={result}");
         return result;
     }
-}
+}

tests/src/JIT/Regression/JitBlue/GitHub_22820/GitHub_22820.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+// Repro for issue 22820. On x86 we need to report enclosed handler
+// live-in locals as live into any enclosing filter.
+//
+// Run with optimized codegen and COMPlus_GCStress=0x4
+
+class DisposableObject : IDisposable
+{
+    public void Dispose()
+    {
+        Console.WriteLine("In dispose");
+    }
+}
+
+class Program
+{
+    public static bool IsExpectedException(Exception e)
+    {
+        Console.WriteLine("In filter");
+        GC.Collect();
+        return e is OperationCanceledException;
+    }
+
+    public static IDisposable AllocateObject()
+    {
+        return new DisposableObject();
+    }
+
+    static int Main(string[] args)
+    {
+        int result = 0;
+
+        try
+        {
+            try
+            {
+                using (AllocateObject())
+                {
+                    throw new Exception();
+                }
+            }
+            catch (Exception e1) when (IsExpectedException(e1))
+            {
+                Console.WriteLine("In catch 1");
+            }
+        }
+        catch (Exception e2)
+        {
+            Console.WriteLine("In catch 2");
+            result = 100;
+        }
+
+        return result;
+    }
+}

tests/src/JIT/Regression/JitBlue/GitHub_22820/GitHub_22820.csproj

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{2649FAFE-07BF-4F93-8120-BA9A69285ABB}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>