[InstCombine] Remove unnecessary byval check in callee cast fold

The logic for handling this was fixed in
8d7f118, but the check for byval
on the callee was retained. This resulted in a weird situation
where the transform would work depending on whether the byval
was only on the call or on both the call and the function.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -3142,8 +3142,7 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
   //
   //  Similarly, avoid folding away bitcasts of byval calls.
   if (Callee->getAttributes().hasAttrSomewhere(Attribute::InAlloca) ||
-      Callee->getAttributes().hasAttrSomewhere(Attribute::Preallocated) ||
-      Callee->getAttributes().hasAttrSomewhere(Attribute::ByVal))
+      Callee->getAttributes().hasAttrSomewhere(Attribute::Preallocated))
     return false;
 
   auto AI = Call.arg_begin();

llvm/test/Transforms/InstCombine/byval.ll

@@ -18,7 +18,8 @@ define void @add_byval(i64* %in) {
 
 define void @add_byval_2(i64* %in) {
 ; CHECK-LABEL: @add_byval_2(
-; CHECK-NEXT:    call void bitcast (void (double*)* @add_byval_callee_2 to void (i64*)*)(i64* byval(i64) [[IN:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i64* [[IN:%.*]] to double*
+; CHECK-NEXT:    call void @add_byval_callee_2(double* byval(double) [[TMP1]])
 ; CHECK-NEXT:    ret void
 ;
   %tmp = bitcast void (double*)* @add_byval_callee_2 to void (i64*)*