JIT: removed unneeded throw helper blocks

src/coreclr/jit/compiler.h

@@ -6295,6 +6295,7 @@ class Compiler
         BasicBlock*     acdDstBlk; // block  to  which we jump
         unsigned        acdData;
         SpecialCodeKind acdKind; // what kind of a special block is this?
+        bool            acdUsed; // do we need to keep this helper block?
 #if !FEATURE_FIXED_OUT_ARGS
         bool     acdStkLvlInit; // has acdStkLvl value been already set?
         unsigned acdStkLvl;     // stack level in stack slots.

src/coreclr/jit/flowgraph.cpp

@@ -3568,6 +3568,10 @@ void Compiler::fgAddCodeRef(BasicBlock* srcBlk, SpecialCodeKind kind)
     add->acdStkLvlInit = false;
 #endif // !FEATURE_FIXED_OUT_ARGS
 
+    // This gets set true in the stack level setter
+    // if there's still a need for this helper
+    add->acdUsed = false;
+
     fgAddCodeList = add;
 
     // Defer creating of the blocks until later.

src/coreclr/jit/stacklevelsetter.cpp

@@ -14,9 +14,9 @@ StackLevelSetter::StackLevelSetter(Compiler* compiler)
     , maxStackLevel(0)
     , memAllocator(compiler->getAllocator(CMK_CallArgs))
     , putArgNumSlots(memAllocator)
+    , throwHelperBlocksUsed(comp->fgUseThrowHelperBlocks() && comp->compUsesThrowHelper)
 #if !FEATURE_FIXED_OUT_ARGS
     , framePointerRequired(compiler->codeGen->isFramePointerRequired())
-    , throwHelperBlocksUsed(comp->fgUseThrowHelperBlocks() && comp->compUsesThrowHelper)
 #endif // !FEATURE_FIXED_OUT_ARGS
 {
     // The constructor reads this value to skip iterations that could set it if it is already set.
@@ -59,8 +59,24 @@ PhaseStatus StackLevelSetter::DoPhase()
     comp->fgSetPtrArgCntMax(maxStackLevel);
     CheckArgCnt();
 
-    // Might want an "other" category for things like this...
-    return PhaseStatus::MODIFIED_NOTHING;
+    // Check if there are any unused throw helper blocks, and if so, remove them.
+    bool madeChanges = false;
+
+    for (Compiler::AddCodeDsc* add = comp->fgGetAdditionalCodeDescriptors(); add != nullptr; add = add->acdNext)
+    {
+        if (add->acdUsed)
+        {
+            continue;
+        }
+
+        BasicBlock* const block = add->acdDstBlk;
+        JITDUMP("Throw help block " FMT_BB " is unused\n", block->bbNum);
+        block->bbFlags &= ~BBF_DONT_REMOVE;
+        comp->fgRemoveBlock(block, /* unreachable */ true);
+        madeChanges = true;
+    }
+
+    return madeChanges ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
 }
 
 //------------------------------------------------------------------------
@@ -89,16 +105,10 @@ void StackLevelSetter::ProcessBlock(BasicBlock* block)
             SubStackLevel(numSlots);
         }
 
-#if !FEATURE_FIXED_OUT_ARGS
-        // Set throw blocks incoming stack depth for x86.
-        if (throwHelperBlocksUsed && !framePointerRequired)
+        if (throwHelperBlocksUsed && node->OperMayThrow(comp))
         {
-            if (node->OperMayThrow(comp))
-            {
-                SetThrowHelperBlocks(node, block);
-            }
+            SetThrowHelperBlocks(node, block);
         }
-#endif // !FEATURE_FIXED_OUT_ARGS
 
         if (node->IsCall())
         {
@@ -112,7 +122,6 @@ void StackLevelSetter::ProcessBlock(BasicBlock* block)
     assert(currentStackLevel == 0);
 }
 
-#if !FEATURE_FIXED_OUT_ARGS
 //------------------------------------------------------------------------
 // SetThrowHelperBlocks: Set throw helper blocks incoming stack levels targeted
 //                       from the node.
@@ -147,6 +156,25 @@ void StackLevelSetter::SetThrowHelperBlocks(GenTree* node, BasicBlock* block)
             SetThrowHelperBlock(SCK_ARITH_EXCPN, block);
             break;
 
+#if defined(TARGET_ARM64) || defined(TARGET_ARM) || defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
+        case GT_DIV:
+        case GT_UDIV:
+        {
+            ExceptionSetFlags exSetFlags = node->OperExceptions(comp);
+
+            if ((exSetFlags & ExceptionSetFlags::DivideByZeroException) != ExceptionSetFlags::None)
+            {
+                SetThrowHelperBlock(SCK_DIV_BY_ZERO, block);
+            }
+
+            if ((exSetFlags & ExceptionSetFlags::ArithmeticException) != ExceptionSetFlags::None)
+            {
+                SetThrowHelperBlock(SCK_ARITH_EXCPN, block);
+            }
+        }
+        break;
+#endif
+
         default: // Other opers can target throw only due to overflow.
             break;
     }
@@ -171,6 +199,11 @@ void StackLevelSetter::SetThrowHelperBlock(SpecialCodeKind kind, BasicBlock* blo
 {
     Compiler::AddCodeDsc* add = comp->fgFindExcptnTarget(kind, comp->bbThrowIndex(block));
     assert(add != nullptr);
+    // We expect we'll actually need this helper.
+    add->acdUsed = true;
+
+#if !FEATURE_FIXED_OUT_ARGS
+
     if (add->acdStkLvlInit)
     {
         // If different range checks happen at different stack levels,
@@ -217,9 +250,8 @@ void StackLevelSetter::SetThrowHelperBlock(SpecialCodeKind kind, BasicBlock* blo
 #endif // Debug
         add->acdStkLvl = currentStackLevel;
     }
-}
-
 #endif // !FEATURE_FIXED_OUT_ARGS
+}
 
 //------------------------------------------------------------------------
 // PopArgumentsFromCall: Calculate the number of stack arguments that are used by the call.

src/coreclr/jit/stacklevelsetter.h

@@ -16,10 +16,8 @@ class StackLevelSetter final : public Phase
 private:
     void ProcessBlock(BasicBlock* block);
 
-#if !FEATURE_FIXED_OUT_ARGS
     void SetThrowHelperBlocks(GenTree* node, BasicBlock* block);
     void SetThrowHelperBlock(SpecialCodeKind kind, BasicBlock* block);
-#endif // !FEATURE_FIXED_OUT_ARGS
 
     unsigned PopArgumentsFromCall(GenTreeCall* call);
     void AddStackLevel(unsigned value);
@@ -35,10 +33,10 @@ class StackLevelSetter final : public Phase
     CompAllocator memAllocator;
 
     typedef JitHashTable<GenTreePutArgStk*, JitPtrKeyFuncs<GenTreePutArgStk>, unsigned> PutArgNumSlotsMap;
-    PutArgNumSlotsMap putArgNumSlots; // The hash table keeps stack slot sizes for active GT_PUTARG_STK nodes.
+    PutArgNumSlotsMap putArgNumSlots;        // The hash table keeps stack slot sizes for active GT_PUTARG_STK nodes.
+    bool              throwHelperBlocksUsed; // Were any throw helper blocks requested for this method.
 
 #if !FEATURE_FIXED_OUT_ARGS
-    bool framePointerRequired;  // Is frame pointer required based on the analysis made by this phase.
-    bool throwHelperBlocksUsed; // Were any throw helper blocks created for this method.
-#endif                          // !FEATURE_FIXED_OUT_ARGS
+    bool framePointerRequired; // Is frame pointer required based on the analysis made by this phase.
+#endif                         // !FEATURE_FIXED_OUT_ARGS
 };