Rollup merge of #147725 - bjorn3:remove_oom_panic, r=Amanieu

Remove -Zoom=panic

There are major questions remaining about the reentrancy that this allows. It doesn't have any users on github outside of a single project that uses it in a panic=abort project to show backtraces. It can still be emulated through `#[alloc_error_handler]` or `set_alloc_error_hook` depending on if you use the standard library or not. And finally it makes it harder to do various improvements to the allocator shim.

With this PR the sole remaining symbol in the allocator shim that is not effectively emulating weak symbols is the symbol that prevents skipping the allocator shim on stable even when it would otherwise be empty because libstd + `#[global_allocator]` is used.

Closes rust-lang/rust#43596
Fixes rust-lang/rust#126683

Author: matthiaskrgr

src/allocator.rs

@@ -1,12 +1,11 @@
 #[cfg(feature = "master")]
 use gccjit::FnAttribute;
-use gccjit::{Context, FunctionType, RValue, ToRValue, Type};
+use gccjit::{Context, FunctionType, ToRValue, Type};
 use rustc_ast::expand::allocator::{
     AllocatorMethod, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE, default_fn_name, global_fn_name,
 };
 use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::config::OomStrategy;
 use rustc_symbol_mangling::mangle_internal_symbol;
 
 use crate::GccContext;
@@ -59,14 +58,6 @@ pub(crate) unsafe fn codegen(
         create_wrapper_function(tcx, context, &from_name, Some(&to_name), &types, output);
     }
 
-    create_const_value_function(
-        tcx,
-        context,
-        &mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
-        i8,
-        context.new_rvalue_from_int(i8, tcx.sess.opts.unstable_opts.oom.should_panic() as i32),
-    );
-
     create_wrapper_function(
         tcx,
         context,
@@ -77,34 +68,6 @@ pub(crate) unsafe fn codegen(
     );
 }
 
-fn create_const_value_function(
-    tcx: TyCtxt<'_>,
-    context: &Context<'_>,
-    name: &str,
-    output: Type<'_>,
-    value: RValue<'_>,
-) {
-    let func = context.new_function(None, FunctionType::Exported, output, &[], name, false);
-
-    #[cfg(feature = "master")]
-    {
-        func.add_attribute(FnAttribute::Visibility(symbol_visibility_to_gcc(
-            tcx.sess.default_visibility(),
-        )));
-
-        // FIXME(antoyo): cg_llvm sets AlwaysInline, but AlwaysInline is different in GCC and using
-        // it here will causes linking errors when using LTO.
-        func.add_attribute(FnAttribute::Inline);
-    }
-
-    if tcx.sess.must_emit_unwind_tables() {
-        // TODO(antoyo): emit unwind tables.
-    }
-
-    let block = func.new_block("entry");
-    block.end_with_return(None, value);
-}
-
 fn create_wrapper_function(
     tcx: TyCtxt<'_>,
     context: &Context<'_>,