[WebAssembly] Don't write SP back when prolog is generated only for EH

Summary:
When we don't actually have stack-allocated variables but need SP only
to support EH, we don't need to write SP back in the epilog, because we
don't bump down the stack pointer.

Reviewers: dschuff

Subscribers: jgravelle-google, sbc100, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D51114

llvm-svn: 340454

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/WebAssembly/exception.ll b/llvm/test/CodeGen/WebAssembly/exception.ll
index a0256d23891..0757f9769bd 100644
--- a/llvm/test/CodeGen/WebAssembly/exception.ll
+++ b/llvm/test/CodeGen/WebAssembly/exception.ll
@@ -217,6 +217,35 @@ ehcleanup:                                        ; preds = %catch
   cleanupret from %8 unwind to caller
 }
 
+; When a function does not have stack-allocated objects, it does not need to
+; store SP back to __stack_pointer global at the epilog.
+
+; CHECK-LABEL: no_sp_writeback
+; CHECK:  try
+; CHECK:  call foo@FUNCTION
+; CHECK:  end_try
+; CHECK-NOT:  set_global  __stack_pointer@GLOBAL
+; CHECK:  return
+define void @no_sp_writeback() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  invoke void @foo()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* null]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call i8* @__cxa_begin_catch(i8* %2) #2 [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %entry, %catch.start
+  ret void
+}
+
 declare void @foo()
 declare void @bar(i32*)
 declare i32 @__gxx_wasm_personality_v0(...)