Rollup merge of #65832 - tlively:emscripten-exception-handling, r=alexcrichton

Re-enable Emscripten's exception handling support

Passes LLVM codegen and Emscripten link-time flags for exception
handling if and only if the panic strategy is `unwind`. Sets the
default panic strategy for Emscripten targets to `unwind`. Re-enables
tests that depend on unwinding support for Emscripten, including
`should_panic` tests.

r? @alexcrichton

1 files changed, 6 insertions, 1 deletions

diff --git a/src/librustc_codegen_llvm/llvm_util.rs b/src/librustc_codegen_llvm/llvm_util.rs
index 2dce9b04c9e..85e0b6d465a 100644
--- a/src/librustc_codegen_llvm/llvm_util.rs
+++ b/src/librustc_codegen_llvm/llvm_util.rs
@@ -3,7 +3,7 @@ use crate::llvm;
 use syntax_pos::symbol::Symbol;
 use rustc::session::Session;
 use rustc::session::config::PrintRequest;
-use rustc_target::spec::MergeFunctions;
+use rustc_target::spec::{MergeFunctions, PanicStrategy};
 use libc::c_int;
 use std::ffi::CString;
 use syntax::feature_gate::UnstableFeatures;
@@ -73,6 +73,11 @@ unsafe fn configure_llvm(sess: &Session) {
             }
         }
 
+        if sess.target.target.target_os == "emscripten" &&
+            sess.panic_strategy() == PanicStrategy::Unwind {
+            add("-enable-emscripten-cxx-exceptions");
+        }
+
         // HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
         // during inlining. Unfortunately these may block other optimizations.
         add("-preserve-alignment-assumptions-during-inlining=false");