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`

Author: matthiaskrgr

src/allocator.rs

@@ -84,19 +84,34 @@ fn codegen_inner(
         &mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind)),
     );
 
-    let data_id = module
-        .declare_data(
-            &mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
-            Linkage::Export,
-            false,
-            false,
-        )
-        .unwrap();
-    let mut data = DataDescription::new();
-    data.set_align(1);
-    let val = oom_strategy.should_panic();
-    data.define(Box::new([val]));
-    module.define_data(data_id, &data).unwrap();
+    {
+        let sig = Signature {
+            call_conv: module.target_config().default_call_conv,
+            params: vec![],
+            returns: vec![AbiParam::new(types::I8)],
+        };
+        let func_id = module
+            .declare_function(
+                &mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
+                Linkage::Export,
+                &sig,
+            )
+            .unwrap();
+        let mut ctx = Context::new();
+        ctx.func.signature = sig;
+        {
+            let mut func_ctx = FunctionBuilderContext::new();
+            let mut bcx = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);
+
+            let block = bcx.create_block();
+            bcx.switch_to_block(block);
+            let value = bcx.ins().iconst(types::I8, oom_strategy.should_panic() as i64);
+            bcx.ins().return_(&[value]);
+            bcx.seal_all_blocks();
+            bcx.finalize();
+        }
+        module.define_function(func_id, &mut ctx).unwrap();
+    }
 
     {
         let sig = Signature {