Take advantage of noreturn attribute to add unreachable instruction &

clear insertion point. The rest of IRgen should theoretically take
advantage of this to avoid emitting dead code. Theory != Practice.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65141 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index d0122fa4f9..02e00558d8 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -1760,6 +1760,18 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
   
   if (const llvm::Function *F = dyn_cast<llvm::Function>(Callee))
     CI->setCallingConv(F->getCallingConv());
+
+  // If the call doesn't return, finish the basic block and clear the
+  // insertion point; this allows the rest of IRgen to discard
+  // unreachable code.
+  if (CI->doesNotReturn()) {
+    Builder.CreateUnreachable();
+    Builder.ClearInsertionPoint();
+
+    // Return a reasonable RValue.
+    return GetUndefRValue(RetTy);
+  }
+
   if (CI->getType() != llvm::Type::VoidTy)
     CI->setName("call");