[PATCH] D48602: `llvm.experimental.stackmap` is erroneously marked `Throws`?

[Edd Barrett via Phabricator via llvm-commits]

vext01 created this revision.
Herald added subscribers: llvm-commits, JDevlieghere.

I've never used phabricator, so sorry if I do this wrong.

This is originally from:
https://bugs.llvm.org/show_bug.cgi?id=37788

---8<---
Over the last few days I have been experimenting with inserting stackmaps from
the Rust compiler.

After inserting some `call`s (not `invoke`s) to llvm.experimental.stackmap into rustc's llvm
codegen, and then allowing the compiler to build itself using this change, I
was surprised to see:

  Cannot invoke an intrinsic other than donothing, patchpoint, statepoint, coro_resume or coro_destroy
  invoke void (i64, i32, ...%) @llvm.experimental.stackmap(i64 1, i32 0)
            to label 13

As I understand, this is LLVM's way of saying, you can't `invoke` (expecting a
possible exception) an intrinsic which cannot raise an exception.

Having spoke to one of the Rust developers about this, and after trying
a few things, it seems that LLVM's inlining pass is itself allowing `call`s to
the stackmap intrinsic to be translated to `invoke`s. Then the verifier rejects
the resulting code.

We suspect that the fix is as follows:

  diff --git a/include/llvm/IR/Intrinsics.td b/include/llvm/IR/Intrinsics.td
  index a2a1f26292c..9bbe22645ac 100644
  --- a/include/llvm/IR/Intrinsics.td
  +++ b/include/llvm/IR/Intrinsics.td
  @@ -720,8 +720,7 @@ def int_invariant_group_barrier : Intrinsic<[llvm_anyptr_ty],
   //===------------------------ Stackmap Intrinsics -------------------------===//
   //
   def int_experimental_stackmap : Intrinsic<[],
  -                                  [llvm_i64_ty, llvm_i32_ty, llvm_vararg_ty],
  -                                  [Throws]>;
  +                                  [llvm_i64_ty, llvm_i32_ty, llvm_vararg_ty], []>;
   def int_experimental_patchpoint_void : Intrinsic<[],
                                                    [llvm_i64_ty, llvm_i32_ty,
                                                     llvm_ptr_ty, llvm_i32_ty,

In other words, remove `Throws` from the signature of `int_experimental_stackmap`.

With this patch applied, I managed to run a stage 2 rustc build without the
verifier getting upset.
--->8---

Since then I've also checked if tests work. They all pass.


Repository:
  rL LLVM

https://reviews.llvm.org/D48602

Files:
  include/llvm/IR/Intrinsics.td


Index: include/llvm/IR/Intrinsics.td
===================================================================
--- include/llvm/IR/Intrinsics.td
+++ include/llvm/IR/Intrinsics.td
@@ -731,8 +731,7 @@
 //===------------------------ Stackmap Intrinsics -------------------------===//
 //
 def int_experimental_stackmap : Intrinsic<[],
-                                  [llvm_i64_ty, llvm_i32_ty, llvm_vararg_ty],
-                                  [Throws]>;
+                                  [llvm_i64_ty, llvm_i32_ty, llvm_vararg_ty], []>;
 def int_experimental_patchpoint_void : Intrinsic<[],
                                                  [llvm_i64_ty, llvm_i32_ty,
                                                   llvm_ptr_ty, llvm_i32_ty,


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