Handle a zero byte cpblk (#24871)

Fix #24846

9 files changed, 108 insertions, 31 deletions

diff --git a/src/jit/codegenlinear.cpp b/src/jit/codegenlinear.cpp
index 88d3ac3b88..dac1df9e56 100644
--- a/src/jit/codegenlinear.cpp
+++ b/src/jit/codegenlinear.cpp
@@ -1662,14 +1662,13 @@ void CodeGen::genSetBlockSize(GenTreeBlk* blkNode, regNumber sizeReg)
     if (sizeReg != REG_NA)
     {
         unsigned blockSize = blkNode->Size();
-        if (blockSize != 0)
+        if (!blkNode->OperIs(GT_STORE_DYN_BLK))
         {
             assert((blkNode->gtRsvdRegs & genRegMask(sizeReg)) != 0);
             genSetRegToIcon(sizeReg, blockSize);
         }
         else
         {
-            noway_assert(blkNode->gtOper == GT_STORE_DYN_BLK);
             GenTree* sizeNode = blkNode->AsDynBlk()->gtDynamicSize;
             if (sizeNode->gtRegNum != sizeReg)
             {
diff --git a/src/jit/codegenxarch.cpp b/src/jit/codegenxarch.cpp
index 0f07cf13e0..3855e2cfe8 100644
--- a/src/jit/codegenxarch.cpp
+++ b/src/jit/codegenxarch.cpp
@@ -3270,25 +3270,19 @@ void CodeGen::genCodeForCpBlkRepMovs(GenTreeBlk* cpBlkNode)
     GenTree* source  = cpBlkNode->Data();
     GenTree* srcAddr = nullptr;
 
-#ifdef DEBUG
     assert(dstAddr->isUsedFromReg());
     assert(source->isContained());
 
 #ifdef _TARGET_X86_
-    if (size == 0)
+    if (!cpBlkNode->OperIs(GT_STORE_DYN_BLK))
     {
-        noway_assert(cpBlkNode->OperGet() == GT_STORE_DYN_BLK);
+        assert((size == 0) || (size > CPBLK_UNROLL_LIMIT));
     }
-    else
-#endif
-    {
-#ifdef _TARGET_AMD64_
-        assert(size > CPBLK_UNROLL_LIMIT && size < CPBLK_MOVS_LIMIT);
-#else
-        assert(size > CPBLK_UNROLL_LIMIT);
+#else // _TARGET_AMD64_
+    // On x64 we use the helper call for GT_STORE_DYN_BLK.
+    assert(!cpBlkNode->OperIs(GT_STORE_DYN_BLK));
+    assert((size == 0) || ((size > CPBLK_UNROLL_LIMIT) && (size < CPBLK_MOVS_LIMIT)));
 #endif
-    }
-#endif // DEBUG
 
     genConsumeBlockOp(cpBlkNode, REG_RDI, REG_RSI, REG_RCX);
     instGen(INS_r_movsb);
@@ -3791,15 +3785,11 @@ void CodeGen::genCodeForCpBlk(GenTreeBlk* cpBlkNode)
     GenTree* srcAddr   = nullptr;
 
     // Size goes in arg2
-    if (blockSize != 0)
+    if (cpBlkNode->gtOper != GT_STORE_DYN_BLK)
     {
         assert(blockSize >= CPBLK_MOVS_LIMIT);
         assert((cpBlkNode->gtRsvdRegs & RBM_ARG_2) != 0);
     }
-    else
-    {
-        noway_assert(cpBlkNode->gtOper == GT_STORE_DYN_BLK);
-    }
 
     // Source address goes in arg1
     if (source->gtOper == GT_IND)
diff --git a/src/jit/gentree.cpp b/src/jit/gentree.cpp
index 420e87c7e5..413db06c05 100644
--- a/src/jit/gentree.cpp
+++ b/src/jit/gentree.cpp
@@ -15456,9 +15456,8 @@ bool GenTree::DefinesLocal(Compiler* comp, GenTreeLclVarCommon** pLclVarTree, bo
         GenTree* destAddr = blkNode->Addr();
         unsigned width    = blkNode->gtBlkSize;
         // Do we care about whether this assigns the entire variable?
-        if (pIsEntire != nullptr && width == 0)
+        if (pIsEntire != nullptr && blkNode->OperIs(GT_DYN_BLK))
         {
-            assert(blkNode->gtOper == GT_DYN_BLK);
             GenTree* blockWidth = blkNode->AsDynBlk()->gtDynamicSize;
             if (blockWidth->IsCnsIntOrI())
             {
diff --git a/src/jit/lowerxarch.cpp b/src/jit/lowerxarch.cpp
index bcb5bef51f..d29ea9375f 100644
--- a/src/jit/lowerxarch.cpp
+++ b/src/jit/lowerxarch.cpp
@@ -329,7 +329,7 @@ void Lowering::LowerBlockStore(GenTreeBlk* blkNode)
         }
         else
         {
-            assert((blkNode->OperGet() == GT_STORE_BLK) || (blkNode->OperGet() == GT_STORE_DYN_BLK));
+            assert(blkNode->OperIs(GT_STORE_BLK, GT_STORE_DYN_BLK));
             // CopyBlk
             // In case of a CpBlk with a constant size and less than CPBLK_MOVS_LIMIT size
             // we can use rep movs to generate code instead of the helper call.
@@ -339,12 +339,12 @@ void Lowering::LowerBlockStore(GenTreeBlk* blkNode)
             unsigned helperThreshold = max(CPBLK_MOVS_LIMIT, CPBLK_UNROLL_LIMIT);
 
             // TODO-X86-CQ: Investigate whether a helper call would be beneficial on x86
-            if ((size != 0) && (size <= helperThreshold))
+            if ((!blkNode->OperIs(GT_STORE_DYN_BLK)) && (size <= helperThreshold))
             {
                 // If we have a buffer between XMM_REGSIZE_BYTES and CPBLK_UNROLL_LIMIT bytes, we'll use SSE2.
                 // Structs and buffer with sizes <= CPBLK_UNROLL_LIMIT bytes are occurring in more than 95% of
                 // our framework assemblies, so this is the main code generation scheme we'll use.
-                if (size <= CPBLK_UNROLL_LIMIT)
+                if ((size != 0) && (size <= CPBLK_UNROLL_LIMIT))
                 {
                     blkNode->gtBlkOpKind = GenTreeBlk::BlkOpKindUnroll;
 
diff --git a/src/jit/lsraarmarch.cpp b/src/jit/lsraarmarch.cpp
index 9a54c32279..cc12e242f3 100644
--- a/src/jit/lsraarmarch.cpp
+++ b/src/jit/lsraarmarch.cpp
@@ -679,7 +679,7 @@ int LinearScan::BuildBlockStore(GenTreeBlk* blkNode)
         }
     }
 
-    if ((size != 0) && (blkSizeRegMask != RBM_NONE))
+    if (!blkNode->OperIs(GT_STORE_DYN_BLK) && (blkSizeRegMask != RBM_NONE))
     {
         // Reserve a temp register for the block size argument.
         buildInternalIntRegisterDefForNode(blkNode, blkSizeRegMask);
@@ -701,9 +701,8 @@ int LinearScan::BuildBlockStore(GenTreeBlk* blkNode)
         BuildUse(dstAddr, dstAddrRegMask);
     }
 
-    if (size == 0)
+    if (blkNode->OperIs(GT_STORE_DYN_BLK))
     {
-        assert(blkNode->OperIs(GT_STORE_DYN_BLK));
         // The block size argument is a third argument to GT_STORE_DYN_BLK
         srcCount++;
         GenTree* blockSize = blkNode->AsDynBlk()->gtDynamicSize;
diff --git a/src/jit/lsraxarch.cpp b/src/jit/lsraxarch.cpp
index 5f1094ee4f..c84a479cd0 100644
--- a/src/jit/lsraxarch.cpp
+++ b/src/jit/lsraxarch.cpp
@@ -1441,7 +1441,7 @@ int LinearScan::BuildBlockStore(GenTreeBlk* blkNode)
         }
     }
 
-    if ((size != 0) && (blkSizeRegMask != RBM_NONE))
+    if (!blkNode->OperIs(GT_STORE_DYN_BLK) && (blkSizeRegMask != RBM_NONE))
     {
         // Reserve a temp register for the block size argument.
         buildInternalIntRegisterDefForNode(blkNode, blkSizeRegMask);
@@ -1463,9 +1463,8 @@ int LinearScan::BuildBlockStore(GenTreeBlk* blkNode)
         BuildUse(dstAddr, dstAddrRegMask);
     }
 
-    if (size == 0)
+    if (blkNode->OperIs(GT_STORE_DYN_BLK))
     {
-        assert(blkNode->OperIs(GT_STORE_DYN_BLK));
         // The block size argument is a third argument to GT_STORE_DYN_BLK
         srcCount++;
         GenTree* blockSize = blkNode->AsDynBlk()->gtDynamicSize;
diff --git a/src/jit/morph.cpp b/src/jit/morph.cpp
index 7040dd0b25..3bfca379a8 100644
--- a/src/jit/morph.cpp
+++ b/src/jit/morph.cpp
@@ -9099,7 +9099,10 @@ GenTree* Compiler::fgMorphOneAsgBlockOp(GenTree* tree)
             size = genTypeSize(asgType);
         }
     }
-    noway_assert((size != 0) || dest->OperIs(GT_DYN_BLK));
+    if (size == 0)
+    {
+        return nullptr;
+    }
 
     //
     //  See if we can do a simple transformation:
diff --git a/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.cs b/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.cs
new file mode 100644
index 0000000000..dbd276f142
--- /dev/null
+++ b/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.cs
@@ -0,0 +1,70 @@
+// 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;
+
+public class GitHub_24846
+{
+    public static void Test(byte[] destination, byte[] source)
+    {
+        Unsafe.CopyBlockUnaligned(ref destination[0], ref source[0], 0);
+    }
+
+    public static int Main(string[] args)
+    {
+        int returnVal = 100;
+        var destination = new byte[1];
+        var source = new byte[1];
+        try
+        {
+            Test(destination, source);
+        }
+        catch (Exception e)
+        {
+            Console.WriteLine("FAILED: " + e.Message);
+            returnVal = -1;
+        }
+        bool caught = false;
+        try
+        {
+            Test(destination, null);
+        }
+        catch (NullReferenceException e)
+        {
+            caught = true;
+        }
+        catch (Exception e)
+        {
+            Console.WriteLine("FAILED: Wrong Exception " + e.Message);
+            returnVal = -1;
+        }
+        if (!caught)
+        {
+            Console.WriteLine("FAILED: null destination didn't throw");
+            returnVal = -1;
+        }
+        caught = false;
+        try
+        {
+            Test(null, source);
+        }
+        catch (NullReferenceException e)
+        {
+            caught = true;
+        }
+        catch (Exception e)
+        {
+            Console.WriteLine("FAILED: Wrong Exception " + e.Message);
+            returnVal = -1;
+        }
+        if (!caught)
+        {
+            Console.WriteLine("FAILED: null source didn't throw");
+            returnVal = -1;
+        }
+        return returnVal;
+    }
+}
+
diff --git a/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.csproj b/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.csproj
new file mode 100644
index 0000000000..fb6ae363eb
--- /dev/null
+++ b/tests/src/JIT/Regression/JitBlue/GitHub_24846/GitHub_24846.csproj
@@ -0,0 +1,18 @@
+<?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=" '$(Configuration)' == '' ">Release</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <AssemblyName>$(MSBuildProjectName)</AssemblyName>
+    <OutputType>Exe</OutputType>
+    <DebugType></DebugType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>