[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, 34 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/WebAssembly/unreachable.ll b/llvm/test/CodeGen/WebAssembly/unreachable.ll
new file mode 100644
index 00000000000..a16e4529033
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/unreachable.ll
@@ -0,0 +1,34 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -fast-isel | FileCheck %s
+
+; Test that LLVM unreachable instruction and trap intrinsic are lowered to
+; wasm unreachable
+
+target datalayout = "e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+declare void @llvm.trap()
+declare void @llvm.debugtrap()
+declare void @abort()
+
+; CHECK-LABEL: f1:
+; CHECK: call $abort
+; CHECK: unreachable
+define i32 @f1() {
+  call void @abort()
+  unreachable
+}
+
+; CHECK-LABEL: f2:
+; CHECK: unreachable
+define void @f2() {
+  call void @llvm.trap()
+  ret void
+}
+
+; CHECK-LABEL: f3:
+; CHECK: unreachable
+define void @f3() {
+  call void @llvm.debugtrap()
+  ret void
+}