[clr-interp] Fix EH logic edge case (#122993)

When a try block exactly encloses another try/finally or try/catch block
and the handler ends at the same point the try body ends we had an off
by one issue in our reprentation of the ilOffset on the leave chain
islands. This fixes the off by one issue for that kind of basic block.
The C# compiler seems to always inject a nop to avoid this issue, but I
do not know why and I can find no justification for that rule.

Fixes badcodeinsidefinally tests

Author: davidwrighton

src/coreclr/interpreter/compiler.cpp

@@ -1097,13 +1097,21 @@ void InterpCompiler::EmitCode()
         getEHinfo(m_methodInfo, i, &clause);
         for (InterpBasicBlock *bb = m_pEntryBB; bb != NULL; bb = bb->pNextBB)
         {
+            if (bb->isLeaveChainIsland && clause.HandlerOffset == (uint32_t)bb->ilOffset)
+            {
+                // Leave chain islands are not part of any EH clause, but their IL offset may be
+               continue;
+            }
+
             if (clause.HandlerOffset <= (uint32_t)bb->ilOffset && (clause.HandlerOffset + clause.HandlerLength) > (uint32_t)bb->ilOffset)
             {
+                INTERP_DUMP("BB %d with ilOffset %x overlaps EH clause %d (handler)\n", bb->index, bb->ilOffset, i);
                 bb->overlappingEHClauseCount++;
             }
 
             if (clause.Flags == CORINFO_EH_CLAUSE_FILTER && clause.FilterOffset <= (uint32_t)bb->ilOffset && clause.HandlerOffset > (uint32_t)bb->ilOffset)
             {
+                INTERP_DUMP("BB %d with ilOffset %x overlaps EH clause %d (filter)\n", bb->index, bb->ilOffset, i);
                 bb->overlappingEHClauseCount++;
             }
         }
@@ -1569,6 +1577,7 @@ void InterpCompiler::GetNativeRangeForClause(uint32_t startILOffset, uint32_t en
     assert(pStartBB != NULL);
 
     InterpBasicBlock* pEndBB = pStartBB;
+
     for (InterpBasicBlock* pBB = pStartBB->pNextBB; (pBB != NULL) && ((uint32_t)pBB->ilOffset < endILOffset); pBB = pBB->pNextBB)
     {
         if (pBB->overlappingEHClauseCount == pStartBB->overlappingEHClauseCount)
@@ -1682,6 +1691,18 @@ void InterpCompiler::BuildEHInfo()
     m_compHnd->setEHcount(nativeEHCount);
 
     unsigned int nativeEHIndex = 0;
+
+#ifdef DEBUG
+    INTERP_DUMP("   BB overlapping EH clause counts:\n");
+    if (t_interpDump)
+    {
+        for (InterpBasicBlock* pBB = GetBB(0); (pBB != NULL); pBB = pBB->pNextBB)
+        {
+            INTERP_DUMP("BB:%d has overlappingEHClauseCount=%d and ilOffset=%x\n", pBB->index, pBB->overlappingEHClauseCount, pBB->ilOffset);
+        }
+    }
+#endif
+
     for (unsigned int i = 0; i < getEHcount(m_methodInfo); i++)
     {
         CORINFO_EH_CLAUSE clause;
@@ -2272,8 +2293,9 @@ void InterpCompiler::CreateLeaveChainIslandBasicBlocks(CORINFO_METHOD_INFO* meth
 
         if (pLeaveChainIslandBB == NULL)
         {
-            pLeaveChainIslandBB = AllocBB(clause.HandlerOffset + clause.HandlerLength);
+            pLeaveChainIslandBB = AllocBB(clause.HandlerOffset);
             pLeaveChainIslandBB->pLeaveTargetBB = pLeaveTargetBB;
+            pLeaveChainIslandBB->isLeaveChainIsland = true;
             *ppLastBBNext = pLeaveChainIslandBB;
         }
 

src/coreclr/interpreter/compiler.h

@@ -335,6 +335,9 @@ struct InterpBasicBlock
     // Valid only for BBs of call islands. It is set to true if it is a finally call island, false if is is a catch leave island.
     bool isFinallyCallIsland;
 
+    // Is a leave chain island basic block
+    bool isLeaveChainIsland;
+
     // If this basic block is a catch or filter funclet entry, this is the index of the variable
     // that holds the exception object.
     int clauseVarIndex;
@@ -366,6 +369,7 @@ struct InterpBasicBlock
         clauseType = BBClauseNone;
         isFilterOrCatchFuncletEntry = false;
         isFinallyCallIsland = false;
+        isLeaveChainIsland = false;
         clauseVarIndex = -1;
         overlappingEHClauseCount = 0;
         enclosingTryBlockCount = -1;