[RPOFuncAttrs] Fix norecurse detection

[aeubanks]

Summary

We wanted to check if all uses of the function are direct calls, but the
code didn't account for passing the function as a parameter.

[nikic]

LGTM

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

static bool addNoRecurseAttrsTopDown(Function &F) {
   // If F is internal and all of its uses are calls from a non-recursive
   // functions, then none of its calls could in fact recurse without going
   // through a function marked norecurse, and so we can mark this function too
   // as norecurse. Note that the uses must actually be calls -- otherwise
   // a pointer to this function could be returned from a norecurse function but
   // this function could be recursively (indirectly) called. Note that this
   // also detects if F is directly recursive as F is not yet marked as
   // a norecurse function.
-  for (auto *U : F.users()) {
-    auto *I = dyn_cast<Instruction>(U);
+  for (auto &U : F.uses()) {
+    auto *I = dyn_cast<Instruction>(U.getUser());
     if (!I)
       return false;
     CallBase *CB = dyn_cast<CallBase>(I);
-    if (!CB || !CB->getParent()->getParent()->doesNotRecurse())
+    if (!CB || !CB->isCallee(&U) ||
+        !CB->getParent()->getParent()->doesNotRecurse())
       return false;
   }
   F.setDoesNotRecurse();
   ++NumNoRecurse;
   return true;
 }
 
 static bool deduceFunctionAttributeInRPO(Module &M, CallGraph &CG) {

llvm/test/Transforms/FunctionAttrs/norecurse.ll

 ; CHECK: Function Attrs
 ; CHECK-NEXT: define void @p
 define void @p() norecurse {
   call void @o()
   ret void
 }
 
 ; CHECK: Function Attrs
-; CHECK-SAME: norecurse nosync readnone
+; CHECK-NOT: norecurse
+; CHECK-SAME: nosync readnone
+; CHECK-NOT: norecurse
 ; CHECK-NEXT: define internal i32 @escapes_as_parameter
 define internal i32 @escapes_as_parameter(ptr %p) {
   %a = call i32 @k()
   ret i32 %a
 }
 ; CHECK: Function Attrs
 ; CHECK-NEXT: define internal void @q
 define internal void @q() {
   %a = call i32 @escapes_as_parameter(ptr @escapes_as_parameter)
   ret void
 }
 ; CHECK: Function Attrs
 ; CHECK-NEXT: define void @r
 define void @r() norecurse {
   call void @q()
   ret void
 }
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