Fix slow tailcalls to VSD (dotnet/coreclr#27363)

* Fix slow tailcalls to VSDs

This was broken when fgCanFastTailCall was changed to call
fgInitArgInfo. fgInitArgInfo has side effects and will in some cases add
arguments to the arg list. Specifically for calls to VSD, the VSD arg is
added, however this case is treated specially for slow tailcalls and it
does not expect the arg to be here.

This targeted fix just removes this arg from the arg list.

* Reenable more_tailcalls on x64 Windows

* Disable more_tailcalls on Unix, arm32 and arm64

* Address feedback

* Disable STRESS_UNSAFE_BUFFER_CHECKS for more_tailcalls


Commit migrated from dotnet/coreclr@f4a8863

src/coreclr/src/jit/morph.cpp

@@ -7412,6 +7412,42 @@ void Compiler::fgMorphTailCallViaHelper(GenTreeCall* call, void* pfnCopyArgs)
     if (call->IsVirtualStub())
     {
         call->gtFlags |= GTF_CALL_NULLCHECK;
+
+#if defined(_TARGET_AMD64_)
+        // If we already inited arg info here then we will have added the VSD
+        // arg on AMD64. So we remove it here as we will handle this case
+        // specially below.
+        fgArgInfo* argInfo = call->fgArgInfo;
+        assert(argInfo != nullptr);
+
+        GenTreeCall::Use* vsdArg = nullptr;
+
+        for (unsigned index = 0; index < argInfo->ArgCount(); ++index)
+        {
+            fgArgTabEntry* arg = argInfo->GetArgEntry(index, false);
+            if (arg->isNonStandard)
+            {
+                // The only supported nonstandard arg for slow tailcalls is
+                // VSD arg.
+                assert(vsdArg == nullptr);
+                vsdArg = arg->use;
+#ifndef DEBUG
+                break;
+#endif
+            }
+        }
+
+        assert(vsdArg != nullptr);
+        // Find the arg in the linked list keeping track of the pointer to it so
+        // we can unlink it.
+        GenTreeCall::Use** ptr = &call->gtCallArgs;
+        while ((*ptr) != vsdArg)
+        {
+            ptr = &(*ptr)->NextRef();
+        }
+
+        *ptr = vsdArg->GetNext();
+#endif
     }
 
 #if defined(_TARGET_ARM_)

src/coreclr/tests/issues.targets

@@ -81,6 +81,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Methodical/tailcall_v4/hijacking/*">
             <Issue>Unix does not support tailcall helper</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/JIT/Directed/tailcall/more_tailcalls/*">
+            <Issue>Unix does not support tailcall helper</Issue>
+        </ExcludeList>
     </ItemGroup>
 
     <!-- Arm32 All OS -->
@@ -233,7 +236,10 @@
             <Issue>26105</Issue>
         </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Methodical/tailcall_v4/hijacking/*">
-            <Issue>arm32 does not support tailcall helper</Issue>
+            <Issue>Unix arm32 does not support tailcall helper</Issue>
+        </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/JIT/Directed/tailcall/more_tailcalls/*">
+            <Issue>Unix arm32 does not support tailcall helper</Issue>
         </ExcludeList>
     </ItemGroup>
 
@@ -281,6 +287,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Methodical/tailcall_v4/hijacking/*">
             <Issue>arm64 does not support tailcall helper</Issue>
         </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/JIT/Directed/tailcall/more_tailcalls/*">
+            <Issue>arm64 does not support tailcall helper</Issue>
+        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_26491/**/*">
             <Issue>26491</Issue>
         </ExcludeList>
@@ -897,12 +906,6 @@
         </ExcludeList>
     </ItemGroup>
 
-    <!-- Tests that run only on x86 Windows -->
-    <ItemGroup Condition="'$(XunitTestBinBase)' != '' and ('$(BuildArch)' != 'x86' or '$(TargetsWindows)' != 'true')">
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Directed/tailcall/more_tailcalls/*">
-            <Issue>x64 Windows has bugs with helper-based tailcall to VSD (#26311); rest of platforms do not support it</Issue>
-        </ExcludeList>
-    </ItemGroup>
     <!-- runtest.proj finds all the *.cmd/*.sh scripts in a test folder and creates corresponding test methods.
          Exclude these scripts to avoid creating such methods for the superpmicollect dependent test projects
          and running them separately from superpmicollect test. -->

src/coreclr/tests/src/JIT/Directed/tailcall/more_tailcalls.ilproj

@@ -9,4 +9,14 @@
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).il" />
   </ItemGroup>
+  <PropertyGroup>
+    <CLRTestBatchPreCommands><![CDATA[
+$(CLRTestBatchPreCommands)
+set COMPlus_JitStressModeNamesNot=STRESS_UNSAFE_BUFFER_CHECKS
+]]></CLRTestBatchPreCommands>
+    <BashCLRTestPreCommands><![CDATA[
+$(BashCLRTestPreCommands)
+export COMPlus_JitStressModeNamesNot=STRESS_UNSAFE_BUFFER_CHECKS
+]]></BashCLRTestPreCommands>
+  </PropertyGroup>
 </Project>