[clang] Missed attribute dereferenceable() for complex argument in stack

[weiguozhi]

Compile the following source code

clang -O3 -fno-exceptions -c test2.cc -o test2.o

#include<string>

char foo(std::string str, int i) {
  return str[i];
}

std::string ha; 
char qux() {
  foo(ha, 3); 
}

I got the following IR

; Function Attrs: mustprogress nounwind uwtable
define dso_local noundef signext i8 @_Z3fooNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEi(ptr noundef %str, i32 noundef %i) #0 {
entry:
  %str.indirect_addr = alloca ptr, align 8
  %i.addr = alloca i32, align 4
  store ptr %str, ptr %str.indirect_addr, align 8, !tbaa !5
  store i32 %i, ptr %i.addr, align 4, !tbaa !10
  %0 = load i32, ptr %i.addr, align 4, !tbaa !10
  %conv = sext i32 %0 to i64
  %call = call noundef nonnull align 1 dereferenceable(1) ptr @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEixEm(ptr noundef nonnull align 8 dereferenceable(32) %str, i64 noundef %conv)
  %1 = load i8, ptr %call, align 1, !tbaa !12
  ret i8 %1 
}

; Function Attrs: mustprogress nounwind uwtable
define dso_local noundef signext i8 @_Z3quxv() #0 {
entry:
  %agg.tmp = alloca %"class.std::__cxx11::basic_string", align 8
  call void @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC2ERKS4_(ptr noundef nonnull align 8 dereferenceable(32) %agg.tmp, ptr noundef nonnull align 8 dereferenceable(32) @_Z2haB5cxx11) 
  %call = call noundef signext i8 @_Z3fooNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEi(ptr noundef %agg.tmp, i32 noundef 3)
  call void @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED2Ev(ptr noundef nonnull align 8 dereferenceable(32) %agg.tmp) #2
  unreachable
} 

The first parameter of foo is of type string, it's too complex, so it is actually allocated in the caller's stack, and the pointer is passed to foo. I expect it has the attribute dereferenceable(32), like the function @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEixEm, but it is missed in function foo.