add a new @llvm.donothing intrinsic that, well, does nothing, and teach CodeGen to ignore calls to it

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159383 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 42 insertions, 1 deletions

diff --git a/include/llvm/Intrinsics.td b/include/llvm/Intrinsics.td
index 8ef4e02..95fd843 100644
--- a/include/llvm/Intrinsics.td
+++ b/include/llvm/Intrinsics.td
@@ -412,6 +412,9 @@ def int_trap : Intrinsic<[], [], [IntrNoReturn]>,
 def int_debugtrap : Intrinsic<[]>,
                     GCCBuiltin<"__builtin_debugtrap">;
 
+// NOP: calls/invokes to this intrinsic are removed by codegen
+def int_donothing : Intrinsic<[], [], [IntrNoMem]>;
+
 // Intrisics to support half precision floating point format
 let Properties = [IntrNoMem] in {
 def int_convert_to_fp16   : Intrinsic<[llvm_i16_ty], [llvm_float_ty]>,
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 0d2d9da..957d00a 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1828,9 +1828,13 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
   MachineBasicBlock *LandingPad = FuncInfo.MBBMap[I.getSuccessor(1)];
 
   const Value *Callee(I.getCalledValue());
+  const Function *Fn = dyn_cast<Function>(Callee);
   if (isa<InlineAsm>(Callee))
     visitInlineAsm(&I);
-  else
+  else if (Fn && Fn->isIntrinsic()) {
+    assert(Fn->getIntrinsicID() == Intrinsic::donothing);
+    return; // ignore invokes to @llvm.donothing
+  } else
     LowerCallTo(&I, getValue(Callee), false, LandingPad);
 
   // If the value of the invoke is used outside of its defining block, make it
@@ -5178,6 +5182,9 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
   case Intrinsic::lifetime_end:
     // Discard region information.
     return 0;
+  case Intrinsic::donothing:
+    // ignore
+    return 0;
   }
 }
 
diff --git a/test/CodeGen/Generic/donothing.ll b/test/CodeGen/Generic/donothing.ll
new file mode 100644
index 0000000..d6ba138
--- /dev/null
+++ b/test/CodeGen/Generic/donothing.ll
@@ -0,0 +1,31 @@
+; RUN: llc < %s | FileCheck %s
+
+declare i32 @__gxx_personality_v0(...)
+declare void @__cxa_call_unexpected(i8*)
+declare void @llvm.donothing() readnone
+
+; CHECK: f1
+define void @f1() nounwind uwtable ssp {
+entry:
+; CHECK-NOT donothing
+  invoke void @llvm.donothing()
+  to label %invoke.cont unwind label %lpad
+
+invoke.cont:
+  ret void
+
+lpad:
+  %0 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
+          filter [0 x i8*] zeroinitializer
+  %1 = extractvalue { i8*, i32 } %0, 0
+  tail call void @__cxa_call_unexpected(i8* %1) noreturn nounwind
+  unreachable
+}
+
+; CHECK: f2
+define void @f2() nounwind {
+entry:
+; CHECK-NOT donothing
+  call void @llvm.donothing()
+  ret void
+}