Set flag in comp info to signal that a caller has >8 byte struct args

src/jit/compiler.h

@@ -8588,8 +8588,9 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         unsigned  compArgsCount;     // Number of arguments (incl. implicit and     hidden)
 
 #if FEATURE_FASTTAILCALL
-        size_t compArgStackSize; // Incoming argument stack size in bytes
-#endif                           // FEATURE_FASTTAILCALL
+        size_t compArgStackSize;     // Incoming argument stack size in bytes
+        bool   compHasMultiSlotArgs; // Caller has >8 byte sized struct parameter
+#endif                               // FEATURE_FASTTAILCALL
 
         unsigned compRetBuffArg; // position of hidden return param var (0, 1) (BAD_VAR_NUM means not present);
         int compTypeCtxtArg; // position of hidden param for type context for generic code (CORINFO_CALLCONV_PARAMTYPE)

src/jit/lclvars.cpp

@@ -364,7 +364,8 @@ void Compiler::lvaInitArgs(InitVarDscInfo* varDscInfo)
     // Save the stack usage information
     // We can get register usage information using codeGen->intRegState and
     // codeGen->floatRegState
-    info.compArgStackSize = varDscInfo->stackArgSize;
+    info.compArgStackSize     = varDscInfo->stackArgSize;
+    info.compHasMultiSlotArgs = varDscInfo->hasMultiSlotStruct;
 #endif // FEATURE_FASTTAILCALL
 
     // The total argument size must be aligned.
@@ -827,8 +828,9 @@ void Compiler::lvaInitUserArgs(InitVarDscInfo* varDscInfo)
                 // If there is a second eightbyte, get a register for it too and map the arg to the reg number.
                 if (structDesc.eightByteCount >= 2)
                 {
-                    secondEightByteType      = GetEightByteType(structDesc, 1);
-                    secondAllocatedRegArgNum = varDscInfo->allocRegArg(secondEightByteType, 1);
+                    secondEightByteType            = GetEightByteType(structDesc, 1);
+                    secondAllocatedRegArgNum       = varDscInfo->allocRegArg(secondEightByteType, 1);
+                    varDscInfo->hasMultiSlotStruct = true;
                 }
 
                 if (secondEightByteType != TYP_UNDEF)
@@ -840,7 +842,8 @@ void Compiler::lvaInitUserArgs(InitVarDscInfo* varDscInfo)
 #ifdef _TARGET_ARM64_
                 if (cSlots == 2)
                 {
-                    varDsc->lvOtherArgReg = genMapRegArgNumToRegNum(firstAllocatedRegArgNum + 1, TYP_I_IMPL);
+                    varDsc->lvOtherArgReg          = genMapRegArgNumToRegNum(firstAllocatedRegArgNum + 1, TYP_I_IMPL);
+                    varDscInfo->hasMultiSlotStruct = true;
                 }
 #endif //  _TARGET_ARM64_
 #endif // defined(UNIX_AMD64_ABI)

src/jit/morph.cpp

@@ -7168,6 +7168,7 @@ bool Compiler::fgCanFastTailCall(GenTreeCall* callee)
     }
 
     const unsigned maxRegArgs = MAX_REG_ARG;
+    hasTwoSlotSizedStruct     = hasTwoSlotSizedStruct || info.compHasMultiSlotArgs;
 
 // If we reached here means that callee has only those argument types which can be passed in
 // a register and if passed on stack will occupy exactly one stack slot in out-going arg area.
@@ -7242,8 +7243,12 @@ bool Compiler::fgCanFastTailCall(GenTreeCall* callee)
         return false;
     }
 
-    // Callee has a >8 and <=16 byte struct and arguments that has to go on the stack. Do not fastTailCall.
-    if (calleeStackSize > 0 && hasTwoSlotSizedStruct)
+    // Either the caller or callee has a >8 and <=16 byte struct and arguments that has to go on the stack. Do not
+    // fastTailCall.
+    //
+    // When either the caller or callee have multi-stlot stack arguments we cannot safely
+    // shuffle arguments in LowerFastTailCall. See https://github.com/dotnet/coreclr/issues/12468.
+    if (hasStackArgs && hasTwoSlotSizedStruct)
     {
         reportFastTailCallDecision("Will not fastTailCall calleeStackSize > 0 && hasTwoSlotSizedStruct",
                                    callerStackSize, calleeStackSize);

src/jit/register_arg_convention.h

@@ -29,6 +29,7 @@ struct InitVarDscInfo
 #if FEATURE_FASTTAILCALL
     // It is used to calculate argument stack size information in byte
     unsigned stackArgSize;
+    bool     hasMultiSlotStruct;
 #endif // FEATURE_FASTTAILCALL
 
 public:
@@ -49,7 +50,8 @@ struct InitVarDscInfo
 #endif // _TARGET_ARM_
 
 #if FEATURE_FASTTAILCALL
-        stackArgSize = 0;
+        stackArgSize       = 0;
+        hasMultiSlotStruct = false;
 #endif // FEATURE_FASTTAILCALL
     }
 

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

@@ -0,0 +1,49 @@
+using System;
+using System.Runtime.CompilerServices;
+
+class X
+{
+    // a -> rdi
+    // b -> rsi
+    // c -> rdx
+    //   -> rcx
+    // d -> r8
+    // e -> r9
+    // f -> s[0]
+    // g -> s[1]
+    public static int F(int a, int b, Guid c, int d, int e, int f, int g)
+    {
+        Guid[] z = new Guid[] { c };
+        // Bug is here passing params to G: f gets trashed by g.
+        return G(a, b, z, d, e, f, g);
+    }
+
+    // loop here is just to make this method too big to inline
+    // if we set [noinline] to effect this, we won't tail call it either.
+    //
+    // a -> rdi
+    // b -> rsi
+    // c -> rdx
+    // d -> rcx
+    // e -> r8
+    // f -> r9
+    // g -> s[0]
+    public static int G(int a, int b, Guid[] c, int d, int e, int f, int g)
+    {
+        int r = 0;
+        for (int i = 0; i < 10; i++)
+        {
+            r += f + g;
+        }
+        return r / 10;
+    }
+
+    // No-opt to stop F from being inlined without marking it noinline
+    [MethodImpl(MethodImplOptions.NoOptimization)]
+    public static int Main()
+    {
+        int result = F(0, 1, Guid.Empty, 3, 4, 33, 67);
+        Console.WriteLine($"Result={result}");
+        return result;
+    }
+}

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