Remove extra UnmanagedCallersOnly overhead on x86 (#46238)

* Implement emitting an unmanaged calling convention entry point with the correct argument order and register usage on x86.

* Move Unix x86 to the UnmanagedCallersOnly plan now that we don't need to do argument shuffling.

* Add SEH hookup and profiler/debugger hooks to Reverse P/Invoke entry helper to match custom x86 thunk.

Fixes #46177

* Remove Windows x86 assembly stub for individual reverse p/invokes. Move Windows x86 unmanaged callers only to not have extra overhead and put reverse P/Invoke stubs for Windows x86 on the UnmanagedCallersOnly plan.

* Further cleanup

* Remove extraneous UnmanagedCallersOnly block now that x86 UnmanagedCallersOnly has been simplified.

* Undo ArgOrder size specifier since it isn't needed and it doesn't work.

* Fix copy constructor reverse marshalling. Now that we don't have the emitted unmanaged thunk stub, we need to handle the x86 differences for copy-constructed parameters in the IL stub.

* Fix version guid syntax.

* Remove FastNExportHandler.

* Revert "Remove FastNExportHandler."

This reverts commit 423f70ee4d564147dc0ce370d38b3a38404f8e22.

* Fix setting up entry frame for new thread.

* Allow the NExportSEH record to live below ESP so we don't need to create a new stack frame.

* Fix formatting.

* Assign an offset for the return buffer on x86 since it might come in on the stack.

* Make sure we use the TC block we just put in on x86 as well.

* Shrink the ReversePInvokeFrame on non-x86 back to master's size.

* Fix arch-specific R2R constant.

* Pass the return address of the ReversePInvokeEnter helper to TraceCall instead of the entry point and call TraceCall from all JIT_ReversePInvokeEnter* helpers.

* Fix ILVerification and ILVerify

* fix R2R constants for crossgen1

* Don't assert ReversePInvokeFrame size for cross-bitness scenarios.

1 files changed, 20 insertions, 4 deletions

diff --git a/src/coreclr/jit/flowgraph.cpp b/src/coreclr/jit/flowgraph.cpp
index 950988adca1..e9cdd48899e 100644
--- a/src/coreclr/jit/flowgraph.cpp
+++ b/src/coreclr/jit/flowgraph.cpp
@@ -8683,13 +8683,29 @@ void Compiler::fgAddReversePInvokeEnterExit()
     varDsc->lvType      = TYP_BLK;
     varDsc->lvExactSize = eeGetEEInfo()->sizeOfReversePInvokeFrame;
 
-    GenTree* tree;
-
     // Add enter pinvoke exit callout at the start of prolog
 
-    tree = gtNewOperNode(GT_ADDR, TYP_I_IMPL, gtNewLclvNode(lvaReversePInvokeFrameVar, TYP_BLK));
+    GenTree* pInvokeFrameVar = gtNewOperNode(GT_ADDR, TYP_I_IMPL, gtNewLclvNode(lvaReversePInvokeFrameVar, TYP_BLK));
+
+    GenTree* stubArgument;
+
+    if (info.compPublishStubParam)
+    {
+        // If we have a secret param for a Reverse P/Invoke, that means that we are in an IL stub.
+        // In this case, the method handle we pass down to the Reverse P/Invoke helper should be
+        // the target method, which is passed in the secret parameter.
+        stubArgument = gtNewLclvNode(lvaStubArgumentVar, TYP_I_IMPL);
+    }
+    else
+    {
+        stubArgument = gtNewIconNode(0, TYP_I_IMPL);
+    }
+
+    GenTree* tree;
+
+    GenTreeCall::Use* args = gtNewCallArgs(pInvokeFrameVar, gtNewIconEmbMethHndNode(info.compMethodHnd), stubArgument);
 
-    tree = gtNewHelperCallNode(CORINFO_HELP_JIT_REVERSE_PINVOKE_ENTER, TYP_VOID, gtNewCallArgs(tree));
+    tree = gtNewHelperCallNode(CORINFO_HELP_JIT_REVERSE_PINVOKE_ENTER, TYP_VOID, args);
 
     fgEnsureFirstBBisScratch();