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Fix silent bad codegen VSD possible tailcall converted to normal call
The problem was when a VSD interface call returning a multi-byte struct in registers was initially considered to be a tailcall, but the tailcall was abandoned in morph due to not enough stack space to store outgoing arguments, in which case we create a new call return local to store the return struct, and re-morph the call. In doing so, we forget that we had already added VSD non-standard args, and re-add them, leaving the originally added arg as a "normal" arg that shouldn't be there. So, in summary, for a call A->B, to see this failure, we need: 1. The call is considered a potential tailcall (by the importer) 2. The call requires non-standard arguments that add call argument IR in fgInitArgInfo() (e.g., VSD call -- in this case, a generic interface call) 3. We reject the tailcall in fgMorphPotentialTailCall() (e.g., not enough incoming arg stack space in A to store B's outgoing args), in this case because the first arg is a large struct. We can't reject it earlier, due to things like address exposed locals -- we must get far enough through the checks to have called fgInitArgInfo() to add the extra non-standard arg. 4. B returns a struct in multiple registers (e.g., a 16-byte struct in Linux x64 ABI) The fix is to remove the previously-added non-standard VSD argument IR when we are preparing to re-morph a call. There was one other location that was already doing this. I'm a little worried that there are other places where the non-standard added IR is not being considered when we clear out the arg info before remorphing. It seems like there is some risk here. Probably, we should consider a better way of handling the non-standard arg IR given the need in some cases to re-morph calls. I commented out a few cases of: ``` assert(!fgCanFastTailCall(call, nullptr)); ``` because this function can call `fgInitArgInfo` which can alter the IR. That seems dangerous in an assert, which should have any side-effects like modifying the IR. Fixes dotnet#49078 No SPMI asm diffs.
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105 changes: 105 additions & 0 deletions
105
src/tests/JIT/Regression/JitBlue/Runtime_49078/Runtime_49078.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,105 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
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| using System; | ||
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| // Regression test for GitHub issue 49078: https://github.com/dotnet/runtime/issues/49078 | ||
| // | ||
| // The problem was when a VSD interface call returning a multi-byte struct in registers was initially considered | ||
| // to be a tailcall, but the tailcall was abandoned in morph due to not enough stack space to store outgoing | ||
| // arguments, in which case we create a new call return local to store the return struct, and re-morph the | ||
| // call. In doing so, we forget that we had already added VSD non-standard args, and re-add them, leaving | ||
| // the originally added arg as a "normal" arg that shouldn't be there. | ||
| // | ||
| // So, in summary, for a call A->B, to see this failure, we need: | ||
| // | ||
| // 1. The call is considered a potential tailcall (by the importer) | ||
| // 2. The call requires non-standard arguments that add call argument IR in fgInitArgInfo() | ||
| // (e.g., VSD call -- in this case, a generic interface call) | ||
| // 3. We reject the tailcall in fgMorphPotentialTailCall() (e.g., not enough incoming arg stack space in A | ||
| // to store B's outgoing args), in this case because the first arg is a large struct. We can't reject | ||
| // it earlier, due to things like address exposed locals -- we must get far enough through the checks | ||
| // to have called fgInitArgInfo() to add the extra non-standard arg. | ||
| // 4. B returns a struct in multiple registers (e.g., a 16-byte struct in Linux x64 ABI) | ||
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| namespace GitHub_49078 | ||
| { | ||
| public struct S16 | ||
| { | ||
| public IntPtr a; | ||
| public uint b; | ||
| } | ||
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| public struct BigStruct | ||
| { | ||
| public IntPtr a, b, c, d, e, f, g, h, j, k, l, m; | ||
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| public BigStruct(IntPtr a1) | ||
| { | ||
| a = b = c = d = e = f = g = h = j = k = l = m = a1; | ||
| } | ||
| } | ||
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| public interface IFoo<T> | ||
| { | ||
| public S16 Foo(BigStruct b, int i, int j); | ||
| } | ||
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| public class CFoo<T> : IFoo<T> | ||
| { | ||
| public S16 Foo(BigStruct b, int i, int j) | ||
| { | ||
| S16 s16; | ||
| s16.a = (IntPtr)i; | ||
| s16.b = (uint)j; | ||
| return s16; | ||
| } | ||
| } | ||
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| class Test | ||
| { | ||
| IFoo<int> m_if = new CFoo<int>(); | ||
| BigStruct m_bs = new BigStruct((IntPtr)1); | ||
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| public S16 Caller(int a) | ||
| { | ||
| // Add some computation so this is not inlineable (but don't mark it noinline, | ||
| // which would prevent the tailcall consideration). | ||
| int i = 7; | ||
| try | ||
| { | ||
| for (int j = 0; j < a; j++) | ||
| { | ||
| i += j; | ||
| } | ||
| } | ||
| finally | ||
| { | ||
| i += 2; | ||
| } | ||
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| return m_if.Foo(m_bs, i, a); | ||
| } | ||
| } | ||
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| class Program | ||
| { | ||
| static int Main(string[] args) | ||
| { | ||
| Test t = new Test(); | ||
| S16 s = t.Caller(4); | ||
| long l = (long)s.a + s.b; | ||
| if (l == 19) | ||
| { | ||
| Console.WriteLine("Passed"); | ||
| return 100; | ||
| } | ||
| else | ||
| { | ||
| Console.WriteLine($"{s.a}, {s.b}, {l}"); | ||
| Console.WriteLine("Failed"); | ||
| return 101; | ||
| } | ||
| } | ||
| } | ||
| } |
14 changes: 14 additions & 0 deletions
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src/tests/JIT/Regression/JitBlue/Runtime_49078/Runtime_49078.csproj
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| @@ -0,0 +1,14 @@ | ||
| <Project Sdk="Microsoft.NET.Sdk"> | ||
| <PropertyGroup> | ||
| <OutputType>Exe</OutputType> | ||
| <CLRTestPriority>1</CLRTestPriority> | ||
| </PropertyGroup> | ||
| <PropertyGroup> | ||
| <AllowUnsafeBlocks>true</AllowUnsafeBlocks> | ||
| <DebugType>None</DebugType> | ||
| <Optimize>True</Optimize> | ||
| </PropertyGroup> | ||
| <ItemGroup> | ||
| <Compile Include="$(MSBuildProjectName).cs" /> | ||
| </ItemGroup> | ||
| </Project> |