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Rollup merge of #69379 - jumbatm:llvm-sigsegv, r=pnkfelix

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Fail on multiple declarations of `main`.

Closes #67946.

Previously, when inserting the entry function, we only checked for
duplicate _definitions_ of `main`.  However, it's possible to cause
problems even only having a duplicate _declaration_. For example,
shadowing `main` using an extern block isn't caught by the current
check, and causes an assertion failure down the line in in LLVM code.

r? @pnkfelix
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Dylan DPC 2020-02-28 01:55:35 +01:00 • committed by GitHub
commit 350491da19
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5 changed files with 31 additions and 4 deletions
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4
src/librustc_codegen_ssa/base.rs
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@ -437,10 +437,10 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
// listing.
let main_ret_ty = cx.tcx().erase_regions(&main_ret_ty.no_bound_vars().unwrap());
if cx.get_defined_value("main").is_some() {
if cx.get_declared_value("main").is_some() {
// FIXME: We should be smart and show a better diagnostic here.
cx.sess()
.struct_span_err(sp, "entry symbol `main` defined multiple times")
.struct_span_err(sp, "entry symbol `main` declared multiple times")
.help("did you use `#[no_mangle]` on `fn main`? Use `#[start]` instead")
.emit();
cx.sess().abort_if_errors();