JIT: Disable TYP_BLK stressing for tail call to loop optimization (#74999)

Fix #57918

src/coreclr/jit/compiler.cpp

@@ -1890,16 +1890,17 @@ void Compiler::compInit(ArenaAllocator*       pAlloc,
         codeGen = nullptr;
     }
 
-    compJmpOpUsed         = false;
-    compLongUsed          = false;
-    compTailCallUsed      = false;
-    compTailPrefixSeen    = false;
-    compLocallocSeen      = false;
-    compLocallocUsed      = false;
-    compLocallocOptimized = false;
-    compQmarkRationalized = false;
-    compQmarkUsed         = false;
-    compFloatingPointUsed = false;
+    compJmpOpUsed                = false;
+    compLongUsed                 = false;
+    compTailCallUsed             = false;
+    compTailPrefixSeen           = false;
+    compMayConvertTailCallToLoop = false;
+    compLocallocSeen             = false;
+    compLocallocUsed             = false;
+    compLocallocOptimized        = false;
+    compQmarkRationalized        = false;
+    compQmarkUsed                = false;
+    compFloatingPointUsed        = false;
 
     compSuppressedZeroInit = false;
 

src/coreclr/jit/compiler.h

@@ -8969,6 +8969,7 @@ public:
     bool compFloatingPointUsed;        // Does the method use TYP_FLOAT or TYP_DOUBLE
     bool compTailCallUsed;             // Does the method do a tailcall
     bool compTailPrefixSeen;           // Does the method IL have tail. prefix
+    bool compMayConvertTailCallToLoop; // Does the method have a recursive tail call that we may convert to a loop?
     bool compLocallocSeen;             // Does the method IL have localloc opcode
     bool compLocallocUsed;             // Does the method use localloc.
     bool compLocallocOptimized;        // Does the method have an optimized localloc

src/coreclr/jit/importer.cpp

@@ -10661,6 +10661,8 @@ DONE:
                     " as having a backward branch.\n",
                     dspTreeID(call), loopHead->bbNum, compCurBB->bbNum);
             fgMarkBackwardJump(loopHead, compCurBB);
+
+            compMayConvertTailCallToLoop = true;
         }
 
         // We only do these OSR checks in the root method because:

src/coreclr/jit/lclvars.cpp

@@ -8406,6 +8406,15 @@ Compiler::fgWalkResult Compiler::lvaStressLclFldCB(GenTree** pTree, fgWalkData*
             return WALK_SKIP_SUBTREES;
         }
 
+        // Converting tail calls to loops may require insertion of explicit
+        // zero initialization for IL locals. The JIT does not support this for
+        // TYP_BLK locals.
+        if (pComp->compMayConvertTailCallToLoop)
+        {
+            varDsc->lvNoLclFldStress = true;
+            return WALK_SKIP_SUBTREES;
+        }
+
         // Fix for lcl_fld stress mode
         if (varDsc->lvKeepType)
         {