[LLVMdev] alias analysis and functions

[dan mihai]

Hi,

I am trying to use alias analysis (Anderson) and noticed that for pointers to functions 
I don't get the expected result: a pointer that clearly may point to a function is 
reported as NoAlias.

I use -anders-aa  -aa-eval -print-no-aliases -print-may-aliases  -print-must-aliases

Here is a test case:

///////////////try_calls_aliases.c 
#include <stdio.h>

typedef int (*PF)();

PF pf01=0;
PF pf2=0;

int pointed_to_function0() {
  printf("pointed_to_function0\n");
  return 1;
}

int pointed_to_function1() {
  pf01 = pointed_to_function1;
  printf("pointed_to_function1\n");
  return 1;
}

void ptr_function_caller(PF pf) {
  printf("ptr_function_caller\n");
  pf();
  PF lpf0 = pointed_to_function0;
  PF lpf1 = pointed_to_function1;
}

int main(int argc, char* argv[]) {
  ptr_function_caller(pointed_to_function0);
  return 0;
}
-------------

After
 llvmgcc  -emit-llvm try_calls_aliases.c  -c -o try_calls_aliases.bc
 opt 2>&1   -anders-aa  -aa-eval -print-no-aliases -print-may-aliases  -print-must-aliases try_calls_aliases.bc | egrep -e 'Alias|Function' > c
I get:
...........
Function: ptr_function_caller: 8 pointers, 2 call sites
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*), i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*)
  NoAlias:    i32 (...)* %pf, i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*) ???????????????????????????????????????????????????????????????????????????????
  NoAlias:    i32 (...)* %pf, i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*)
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*), i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*), i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)* %pf, i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*), i32 (...)** %pf_addr
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*), i32 (...)** %pf_addr
  NoAlias:    i32 (...)* %pf, i32 (...)** %pf_addr
  NoAlias:    i32 (...)** %pf_addr, i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*), i32 (...)** %lpf1
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*), i32 (...)** %lpf1
  NoAlias:    i32 (...)* %pf, i32 (...)** %lpf1
  NoAlias:    i32 (...)** %lpf1, i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)** %lpf1, i32 (...)** %pf_addr
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*), i32 (...)** %lpf0
  NoAlias:    i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*), i32 (...)** %lpf0
  NoAlias:    i32 (...)* %pf, i32 (...)** %lpf0
  NoAlias:    i32 (...)** %lpf0, i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)** %lpf0, i32 (...)** %pf_addr
  NoAlias:    i32 (...)** %lpf0, i32 (...)** %lpf1
  NoAlias:    i32 (...)* %1, i32 (...)* bitcast (i32 ()* @pointed_to_function0 to i32 (...)*)
  NoAlias:    i32 (...)* %1, i32 (...)* bitcast (i32 ()* @pointed_to_function1 to i32 (...)*)
  MayAlias:    i32 (...)* %1, i32 (...)* %pf
  NoAlias:    i32 (...)* %1, i8* getelementptr ([20 x i8]* @.str2, i32 0, i64 0)
  NoAlias:    i32 (...)* %1, i32 (...)** %pf_addr
  NoAlias:    i32 (...)* %1, i32 (...)** %lpf1
  NoAlias:    i32 (...)* %1, i32 (...)** %lpf0
...............

Any advice on how to get this work as expected? (that is pf MayAlias pointed_to_function0 inside ptr_function_caller, etc)?

Thank you,
Dan


 		 	   		  
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