Rollup merge of rust-lang#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#43596
Fixes rust-lang#126683

Author: matthiaskrgr

src/allocator.rs

@@ -6,7 +6,6 @@ use rustc_ast::expand::allocator::{
     AllocatorMethod, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE, default_fn_name, global_fn_name,
 };
 use rustc_codegen_ssa::base::{allocator_kind_for_codegen, allocator_shim_contents};
-use rustc_session::config::OomStrategy;
 use rustc_symbol_mangling::mangle_internal_symbol;
 
 use crate::prelude::*;
@@ -15,16 +14,11 @@ use crate::prelude::*;
 pub(crate) fn codegen(tcx: TyCtxt<'_>, module: &mut dyn Module) -> bool {
     let Some(kind) = allocator_kind_for_codegen(tcx) else { return false };
     let methods = allocator_shim_contents(tcx, kind);
-    codegen_inner(tcx, module, &methods, tcx.sess.opts.unstable_opts.oom);
+    codegen_inner(tcx, module, &methods);
     true
 }
 
-fn codegen_inner(
-    tcx: TyCtxt<'_>,
-    module: &mut dyn Module,
-    methods: &[AllocatorMethod],
-    oom_strategy: OomStrategy,
-) {
+fn codegen_inner(tcx: TyCtxt<'_>, module: &mut dyn Module, methods: &[AllocatorMethod]) {
     let usize_ty = module.target_config().pointer_type();
 
     for method in methods {
@@ -65,35 +59,6 @@ fn codegen_inner(
         );
     }
 
-    {
-        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 {
             call_conv: module.target_config().default_call_conv,