[WebAssembly] Support 'unreachable' expression

Lower LLVM's 'unreachable' terminator to ISD::TRAP, and lower ISD::TRAP to
wasm's 'unreachable' expression.

WebAssembly type-checks expressions, but a noreturn function with a
return type that doesn't match the context will cause a check
failure. So we lower LLVM 'unreachable' to ISD::TRAP and then lower that
to WebAssembly's 'unreachable' expression, which typechecks in any
context and causes a trap if executed.

Differential Revision: http://reviews.llvm.org/D14515

llvm-svn: 252566

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
index a7e87f9d04d..6aae5d38d0b 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
@@ -54,10 +54,14 @@ multiclass RETURN<WebAssemblyRegClass vt> {
   def RETURN_#vt : I<(outs), (ins vt:$val), [(WebAssemblyreturn vt:$val)],
                      "return $val">;
 }
-let isReturn = 1, isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
+
+let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
+let isReturn = 1 in {
   defm : RETURN<I32>;
   defm : RETURN<I64>;
   defm : RETURN<F32>;
   defm : RETURN<F64>;
   def RETURN_VOID : I<(outs), (ins), [(WebAssemblyreturn)], "return">;
-} // isReturn = 1, isTerminator = 1, hasCtrlDep = 1, isBarrier = 1
+} // isReturn = 1
+  def UNREACHABLE : I<(outs), (ins), [(trap)], "unreachable">;
+} // isTerminator = 1, hasCtrlDep = 1, isBarrier = 1