[Bug tree-optimization/42586] load-modify-store on x86 should be a single instruction

[andi-gcc at firstfloor dot org]

------- Comment #19 from andi-gcc at firstfloor dot org  2010-01-03 13:18 
-------

Here's another example with the bogus stack frame problem with a tail call
(the embarassing website has quite a lot of similar cases, normally
near the tail of the tables with 16 vs 22 bytes e.g. against sun cc
which also does tail optimization):


typedef long __clock_t;

typedef __clock_t clock_t;

struct lprofS_sSTACK_RECORD;

typedef struct lprofS_sSTACK_RECORD lprofS_STACK_RECORD;

struct lprofS_sSTACK_RECORD

{

  clock_t time_marker_function_local_time;

  clock_t time_marker_function_total_time;

  char *file_defined;

  char *function_name;

  char *source_code;

  long line_defined;

  long current_line;

  float local_time;

  float total_time;

  lprofS_STACK_RECORD *next;

};

typedef lprofS_STACK_RECORD *lprofS_STACK;

struct lprofP_sSTATE;

typedef struct lprofP_sSTATE lprofP_STATE;

struct lprofP_sSTATE

{

  int stack_level;

  lprofS_STACK stack_top;

};

extern void lprofC_start_timer (clock_t * time_marker);

void lprofM_resume_local_time (lprofP_STATE * S);

void

lprofM_resume_local_time (lprofP_STATE * S)

{



  {

    lprofC_start_timer (&(S->stack_top)->time_marker_function_local_time);

    return;

  }

}

gives with -m32 -fomit-frame-pointer -O2 and 4.5.0 20091219

 subl    $12, %esp
        movl    16(%esp), %eax
        movl    4(%eax), %eax
        movl    %eax, 16(%esp)
        addl    $12, %esp
        jmp     lprofC_start_timer

The subl/addl are completely unnecessary


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42586