Rollup merge of #143387 - dpaoliello:shouldpanicfn, r=bjorn3

Make __rust_alloc_error_handler_should_panic a function

Fixes rust-lang/rust#143253

`__rust_alloc_error_handler_should_panic` is a static but was being exported as a function.

For most targets this doesn't matter, but Arm64EC Windows uses different decorations for exported variables vs functions, hence it fails to link when `-Z oom=abort` is enabled.

We've had issues in the past with statics like this (see rust-lang/rust#141061) but the tldr; is that Arm64EC needs symbols correctly exported as either a function or data, and data MUST and MUST ONLY be marked `dllimport` when the symbol is being imported from another binary, which is non-trivial to calculate for these compiler-generated statics.

So, instead, the easiest thing to do is to make `__rust_alloc_error_handler_should_panic` a function instead.

Since `__rust_alloc_error_handler_should_panic` isn't involved in any linking shenanigans, I've marked it as `AlwaysInline` with the hopes that the various backends will see that it is just returning a constant and perform the same optimizations as the previous implementation.

r? `@bjorn3`

1 files changed, 37 insertions, 8 deletions

diff --git a/compiler/rustc_codegen_llvm/src/allocator.rs b/compiler/rustc_codegen_llvm/src/allocator.rs
index 9dca63cfc8d..2b5090ed6db 100644
--- a/compiler/rustc_codegen_llvm/src/allocator.rs
+++ b/compiler/rustc_codegen_llvm/src/allocator.rs
@@ -11,7 +11,7 @@ use rustc_symbol_mangling::mangle_internal_symbol;
 
 use crate::builder::SBuilder;
 use crate::declare::declare_simple_fn;
-use crate::llvm::{self, False, True, Type};
+use crate::llvm::{self, False, True, Type, Value};
 use crate::{SimpleCx, attributes, debuginfo};
 
 pub(crate) unsafe fn codegen(
@@ -73,13 +73,14 @@ pub(crate) unsafe fn codegen(
     );
 
     unsafe {
-        // __rust_alloc_error_handler_should_panic
-        let name = mangle_internal_symbol(tcx, OomStrategy::SYMBOL);
-        let ll_g = cx.declare_global(&name, i8);
-        llvm::set_visibility(ll_g, llvm::Visibility::from_generic(tcx.sess.default_visibility()));
-        let val = tcx.sess.opts.unstable_opts.oom.should_panic();
-        let llval = llvm::LLVMConstInt(i8, val as u64, False);
-        llvm::set_initializer(ll_g, llval);
+        // __rust_alloc_error_handler_should_panic_v2
+        create_const_value_function(
+            tcx,
+            &cx,
+            &mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
+            &i8,
+            &llvm::LLVMConstInt(i8, tcx.sess.opts.unstable_opts.oom.should_panic() as u64, False),
+        );
 
         // __rust_no_alloc_shim_is_unstable_v2
         create_wrapper_function(
@@ -100,6 +101,34 @@ pub(crate) unsafe fn codegen(
     }
 }
 
+fn create_const_value_function(
+    tcx: TyCtxt<'_>,
+    cx: &SimpleCx<'_>,
+    name: &str,
+    output: &Type,
+    value: &Value,
+) {
+    let ty = cx.type_func(&[], output);
+    let llfn = declare_simple_fn(
+        &cx,
+        name,
+        llvm::CallConv::CCallConv,
+        llvm::UnnamedAddr::Global,
+        llvm::Visibility::from_generic(tcx.sess.default_visibility()),
+        ty,
+    );
+
+    attributes::apply_to_llfn(
+        llfn,
+        llvm::AttributePlace::Function,
+        &[llvm::AttributeKind::AlwaysInline.create_attr(cx.llcx)],
+    );
+
+    let llbb = unsafe { llvm::LLVMAppendBasicBlockInContext(cx.llcx, llfn, c"entry".as_ptr()) };
+    let mut bx = SBuilder::build(&cx, llbb);
+    bx.ret(value);
+}
+
 fn create_wrapper_function(
     tcx: TyCtxt<'_>,
     cx: &SimpleCx<'_>,