[Bug tree-optimization/33302] New: follow-up on bug 33291 dead-store not eliminated

["wouter dot vermaelen at scarlet dot be" <gcc-bugzilla at gcc dot gnu dot org>]

This is a follow-up on bug 33291. It uses the same testcase (repeated here) but
with some additional optimization flags.

-------------------------------------------
struct Clock {
 void f();
 void add(unsigned n) { a += n; }
 int a;
};

struct CPU : Clock {
 virtual ~CPU();
 unsigned char readSlow();
 void execute();

 void delay() { add(2); }
 unsigned char readFast() {
  if (unsigned char* p = ptrs[addr >> 8]) {
   // fast-path
   delay();
   delay();
   return p[addr & 255];
  } else {
   // slow-path
   return readSlow();
  }
 }

 typedef void (CPU::*FuncPtr)();
 static FuncPtr tab[256];
 unsigned char* ptrs[256];
 unsigned addr;
};

void CPU::execute() {
 f();
 while (true) {
  unsigned char b = readFast();
  delay();
  (this->*tab[b])();
 }
}
----------------------------------------

When compiled with SVN revision 128074 on a linux x86_64 machine:

> g++ -O3 -fforce-addr -ftracer -S CPU.ii
> cat CPU.s
    ...
    movl    (%rbx), %eax
    leal    4(%rax), %edx
    addl    $6, %eax
    movl    %edx, (%rbx)       #### dead store
    movzbl  (%r12), %edx
    movzbl  (%rcx,%rdx), %edx
    movl    %eax, (%rbx)
    ...


-- 
           Summary: follow-up on bug 33291   dead-store not eliminated
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: wouter dot vermaelen at scarlet dot be


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33302