Rollup merge of #103977 - TimNN:memory-effects, r=nikic

LLVM 16: Switch to using MemoryEffects

This adapts the compiler to the changes required by https://github.com/llvm/llvm-project/commit/304f1d59ca41872c094def3aee0a8689df6aa398.

AFAICT, `WriteOnly` isn't used by the compiler, all `ReadNone` uses were migrated and the remaining use of `ReadOnly` is only for function parameters.

To simplify the FFI, this PR uses an enum to represent `MemoryEffects` across the FFI boundary, which then gets mapped to the matching static factory method when constructing the attribute.

Fixes #103961.

`@rustbot` label +llvm-main

r? `@nikic`

1 files changed, 40 insertions, 2 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index 6f36281af23..0d9b5a57b69 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -8,6 +8,9 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/IntrinsicsARM.h"
 #include "llvm/IR/Mangler.h"
+#if LLVM_VERSION_GE(16, 0)
+#include "llvm/IR/ModRef.h"
+#endif
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/COFFImportFile.h"
 #include "llvm/Object/ObjectFile.h"
@@ -213,8 +216,6 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
     return Attribute::ReturnsTwice;
   case ReadNone:
     return Attribute::ReadNone;
-  case InaccessibleMemOnly:
-    return Attribute::InaccessibleMemOnly;
   case SanitizeHWAddress:
     return Attribute::SanitizeHWAddress;
   case WillReturn:
@@ -379,6 +380,43 @@ extern "C" LLVMAttributeRef LLVMRustCreateAllocKindAttr(LLVMContextRef C, uint64
 #endif
 }
 
+// Simplified representation of `MemoryEffects` across the FFI boundary.
+//
+// Each variant corresponds to one of the static factory methods on `MemoryEffects`.
+enum class LLVMRustMemoryEffects {
+  None,
+  ReadOnly,
+  InaccessibleMemOnly,
+};
+
+extern "C" LLVMAttributeRef LLVMRustCreateMemoryEffectsAttr(LLVMContextRef C,
+                                                            LLVMRustMemoryEffects Effects) {
+#if LLVM_VERSION_GE(16, 0)
+  switch (Effects) {
+    case LLVMRustMemoryEffects::None:
+      return wrap(Attribute::getWithMemoryEffects(*unwrap(C), MemoryEffects::none()));
+    case LLVMRustMemoryEffects::ReadOnly:
+      return wrap(Attribute::getWithMemoryEffects(*unwrap(C), MemoryEffects::readOnly()));
+    case LLVMRustMemoryEffects::InaccessibleMemOnly:
+      return wrap(Attribute::getWithMemoryEffects(*unwrap(C),
+                                                  MemoryEffects::inaccessibleMemOnly()));
+    default:
+      report_fatal_error("bad MemoryEffects.");
+  }
+#else
+  switch (Effects) {
+    case LLVMRustMemoryEffects::None:
+      return wrap(Attribute::get(*unwrap(C), Attribute::ReadNone));
+    case LLVMRustMemoryEffects::ReadOnly:
+      return wrap(Attribute::get(*unwrap(C), Attribute::ReadOnly));
+    case LLVMRustMemoryEffects::InaccessibleMemOnly:
+      return wrap(Attribute::get(*unwrap(C), Attribute::InaccessibleMemOnly));
+    default:
+      report_fatal_error("bad MemoryEffects.");
+  }
+#endif
+}
+
 // Enable a fast-math flag
 //
 // https://llvm.org/docs/LangRef.html#fast-math-flags