Do not derive no-recurse attribute if function does not have exact definition.

[vivekvpandya]

Summary

This is fix for https://bugs.llvm.org/show_bug.cgi?id=41336

[jdoerfert]

LGTM. Though I hope to remove the FunctionAttr code soonish.

[vivekvpandya]

In D63045#1535246, @jdoerfert wrote:

LGTM. Though I hope to remove the FunctionAttr code soonish.

If this code will be removed do we need to commit this?
if yes then is my testing enough?
I have tested this change with check-all (where my build has all targets, clang project enabled)
I am missing anything on testing?

[jdoerfert]

In D63045#1535255, @vivekvpandya wrote:

In D63045#1535246, @jdoerfert wrote:

LGTM. Though I hope to remove the FunctionAttr code soonish.

If this code will be removed do we need to commit this?

We should.

if yes then is my testing enough?

I think so.

I have tested this change with check-all (where my build has all targets, clang project enabled)

Good.

I am missing anything on testing?

No.

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

 static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
   // Try and identify functions that do not recurse.
 
   // If the SCC contains multiple nodes we know for sure there is recursion.
   if (SCCNodes.size() != 1)
     return false;
 
   Function *F = *SCCNodes.begin();
-  if (!F || F->isDeclaration() || F->doesNotRecurse())
+  if (!F || !F->hasExactDefinition() || F->doesNotRecurse())
     return false;
 
   // If all of the calls in F are identifiable and are to norecurse functions, F
   // is norecurse. This check also detects self-recursion as F is not currently
   // marked norecurse, so any called from F to F will not be marked norecurse.
   for (auto &BB : *F)
     for (auto &I : BB.instructionsWithoutDebug())
       if (auto CS = CallSite(&I)) {

llvm/test/Transforms/FunctionAttrs/arg_returned.ll

 ;
 ;  int *calls_maybe_redefined_fn(int *r) {
 ;    maybe_redefined_fn(r);
 ;    return r;
 ;  }
 ;
 ; Verify the maybe-redefined function is not annotated:
 ;
-; CHECK: Function Attrs: noinline norecurse nounwind uwtable
+; CHECK: Function Attrs: noinline nounwind uwtable
 ; CHECK: define linkonce_odr i32* @maybe_redefined_fn(i32* %r)
-; FIXME: We should not derive norecurse for potentially redefined functions!
-;        Function Attrs: noinline nounwind uwtable
-;        define linkonce_odr i32* @maybe_redefined_fn(i32* %r)
 ;
-; CHECK: Function Attrs: noinline norecurse nounwind uwtable
+; CHECK: Function Attrs: noinline nounwind uwtable
 ; CHECK: define i32* @calls_maybe_redefined_fn(i32* returned %r)
-; FIXME: We should not derive norecurse for potentially redefined functions!
-;        Function Attrs: noinline nounwind uwtable
-;        define i32* @calls_maybe_redefined_fn(i32* returned %r)
 define linkonce_odr i32* @maybe_redefined_fn(i32* %r) #0 {
 entry:
   ret i32* %r
 }
 
 define i32* @calls_maybe_redefined_fn(i32* %r) #0 {
 entry:
   %call = call i32* @maybe_redefined_fn(i32* %r)

 
 attributes #0 = { noinline nounwind uwtable }
 
 ; CHECK-NOT: attributes #
 ; CHECK-DAG: attributes #{{[0-9]*}} = { noinline norecurse nounwind readnone uwtable }
 ; CHECK-DAG: attributes #{{[0-9]*}} = { noinline nounwind readnone uwtable }
 ; CHECK-DAG: attributes #{{[0-9]*}} = { noinline nounwind readonly uwtable }
 ; CHECK-DAG: attributes #{{[0-9]*}} = { noinline nounwind uwtable }
-; CHECK-DAG: attributes #{{[0-9]*}} = { noinline norecurse nounwind uwtable }
 ; CHECK-NOT: attributes #