[IR] Fix incorrect writeonly on llvm.allow.ubsan/runtime.check (#145492)

These intrinsics introduced in #84850 are currently marked as
`memory(inaccessiblemem: write)`. This is not correct for the intended
purpose of allowing per-block decisions, as such calls may get DCEd
across control-flow boundaries (which will start actually happening with
#145474).

Use `memory(inaccessiblemem: readwrite)` instead, just like all the
other control-flow sensitive intrinsics.

Author: nikic

llvm/include/llvm/IR/Intrinsics.td

@@ -1842,11 +1842,11 @@ def int_ubsantrap : Intrinsic<[], [llvm_i8_ty],
 
 // Return true if ubsan check is allowed.
 def int_allow_ubsan_check : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_i8_ty],
-    [IntrInaccessibleMemOnly, IntrWriteMem, ImmArg<ArgIndex<0>>, NoUndef<RetIndex>]>;
+    [IntrInaccessibleMemOnly, ImmArg<ArgIndex<0>>, NoUndef<RetIndex>]>;
 
 // Return true if runtime check is allowed.
 def int_allow_runtime_check : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_metadata_ty],
-    [IntrInaccessibleMemOnly, IntrWriteMem, NoUndef<RetIndex>]>,
+    [IntrInaccessibleMemOnly, NoUndef<RetIndex>]>,
     ClangBuiltin<"__builtin_allow_runtime_check">;
 
 // Support for dynamic deoptimization (or de-specialization)

llvm/test/Instrumentation/BoundsChecking/runtimes.ll

@@ -205,7 +205,7 @@ define void @f1(i64 %x) nounwind {
 ; TR-GUARD: attributes #[[ATTR3]] = { nomerge noreturn nounwind }
 ;.
 ; RT-GUARD: attributes #[[ATTR0]] = { nounwind }
-; RT-GUARD: attributes #[[ATTR1:[0-9]+]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) }
+; RT-GUARD: attributes #[[ATTR1:[0-9]+]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
 ; RT-GUARD: attributes #[[ATTR2]] = { nomerge nounwind }
 ;.
 ; TR: [[META0]] = !{}