[FunctionAttrs] Don't try to infer returned if it is already on an ar…

…gument

Trying to infer the 'returned' attribute if an argument is already
'returned' can lead to verification failure: inference might determine
that a different argument is passed through which would result in two
different arguments marked as 'returned'.

This fixes PR30350.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281221 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/FunctionAttrs.cpp

@@ -496,6 +496,11 @@ static bool addArgumentReturnedAttrs(const SCCNodeSet &SCCNodes) {
     if (F->getReturnType()->isVoidTy())
       continue;
 
+    // There is nothing to do if an argument is already marked as 'returned'.
+    if (any_of(F->args(),
+               [](const Argument &Arg) { return Arg.hasReturnedAttr(); }))
+      continue;
+
     auto FindRetArg = [&]() -> Value * {
       Value *RetArg = nullptr;
       for (BasicBlock &BB : *F)

test/Transforms/FunctionAttrs/returned.ll

@@ -16,3 +16,15 @@ lor.lhs.false:                                    ; preds = %entry
 cond.end:                                         ; preds = %entry
   ret i32 %p
 }
+
+; CHECK: define i32 @test2(i32 %p1, i32 returned %p2)
+define i32 @test2(i32 %p1, i32 returned %p2) {
+  %_tmp4 = icmp eq i32 %p1, %p2
+  br i1 %_tmp4, label %bb2, label %bb1
+
+bb2:                                              ; preds = %0
+  ret i32 %p1
+
+bb1:                                              ; preds = %bb1, %0
+  br label %bb1
+}