Don't emit an unreachable return block.

Patch by Brad Moody.

llvm-svn: 358104

clang/lib/CodeGen/CGCall.cpp

@@ -2873,15 +2873,6 @@ void CodeGenFunction::EmitFunctionEpilog(const CGFunctionInfo &FI,
         RV = SI->getValueOperand();
         SI->eraseFromParent();
 
-        // If that was the only use of the return value, nuke it as well now.
-        auto returnValueInst = ReturnValue.getPointer();
-        if (returnValueInst->use_empty()) {
-          if (auto alloca = dyn_cast<llvm::AllocaInst>(returnValueInst)) {
-            alloca->eraseFromParent();
-            ReturnValue = Address::invalid();
-          }
-        }
-
       // Otherwise, we have to do a simple load.
       } else {
         RV = Builder.CreateLoad(ReturnValue);

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -255,6 +255,7 @@ llvm::DebugLoc CodeGenFunction::EmitReturnBlock() {
     if (CurBB->empty() || ReturnBlock.getBlock()->use_empty()) {
       ReturnBlock.getBlock()->replaceAllUsesWith(CurBB);
       delete ReturnBlock.getBlock();
+      ReturnBlock = JumpDest();
     } else
       EmitBlock(ReturnBlock.getBlock());
     return llvm::DebugLoc();
@@ -274,6 +275,7 @@ llvm::DebugLoc CodeGenFunction::EmitReturnBlock() {
       Builder.SetInsertPoint(BI->getParent());
       BI->eraseFromParent();
       delete ReturnBlock.getBlock();
+      ReturnBlock = JumpDest();
       return Loc;
     }
   }
@@ -448,6 +450,19 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
   // 5. Width of vector aguments and return types for functions called by this
   //    function.
   CurFn->addFnAttr("min-legal-vector-width", llvm::utostr(LargestVectorWidth));
+
+  // If we generated an unreachable return block, delete it now.
+  if (ReturnBlock.isValid() && ReturnBlock.getBlock()->use_empty()) {
+    Builder.ClearInsertionPoint();
+    ReturnBlock.getBlock()->eraseFromParent();
+  }
+  if (ReturnValue.isValid()) {
+    auto *RetAlloca = dyn_cast<llvm::AllocaInst>(ReturnValue.getPointer());
+    if (RetAlloca && RetAlloca->use_empty()) {
+      RetAlloca->eraseFromParent();
+      ReturnValue = Address::invalid();
+    }
+  }
 }
 
 /// ShouldInstrumentFunction - Return true if the current function should be

clang/test/CodeGen/unreachable-ret.c

@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+
+extern void abort() __attribute__((noreturn));
+
+void f1() {
+  abort();
+}
+// CHECK-LABEL: define void @f1()
+// CHECK-NEXT: entry:
+// CHECK-NEXT:   call void @abort()
+// CHECK-NEXT:   unreachable
+// CHECK-NEXT: }
+
+void *f2() {
+  abort();
+  return 0;
+}
+// CHECK-LABEL: define i8* @f2()
+// CHECK-NEXT: entry:
+// CHECK-NEXT:   call void @abort()
+// CHECK-NEXT:   unreachable
+// CHECK-NEXT: }
+

clang/test/OpenMP/parallel_reduction_codegen.cpp

@@ -622,7 +622,7 @@ int main() {
 
 // CHECK-NOT: call i32 @__kmpc_reduce
 
-// CHECK: ret void
+// CHECK: }
 
 // CHECK: define {{.*}} i{{[0-9]+}} [[TMAIN_INT]]()
 // CHECK: [[TEST:%.+]] = alloca [[S_INT_TY]],