[Bug tree-optimization/54492] New: [4.8 Regression] SLSR takes ages

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54492

             Bug #: 54492
           Summary: [4.8 Regression] SLSR takes ages
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: rgue...@gcc.gnu.org
                CC: wschm...@gcc.gnu.org


For

int foo (int a, int b, int c)
{
  int d;
  switch (a)
    {
#define X(N) \
    case N ## 0: d = a + b; break; \
    case N ## 1: d = a + b; break; \
    case N ## 2: d = a + b; break; \
    case N ## 3: d = a + b; break; \
    case N ## 4: d = a + b; break; \
    case N ## 5: d = a + b; break; \
    case N ## 6: d = a + b; break; \
    case N ## 7: d = a + b; break; \
    case N ## 8: d = a + b; break; \
    case N ## 9: d = a + b; break;
#define XX(N) \
    X(N ## 0) X(N ## 1) X(N ## 2) X(N ## 3) X(N ## 4) X(N ## 5) X(N ## 6) X(N
## 7) X(N ## 8) X(N ## 9)
#define XXX(N) \
    XX(N ## 0) XX(N ## 1) XX(N ## 2) XX(N ## 3) XX(N ## 4) XX(N ## 5) XX(N ##
6) XX(N ## 7) XX(N ## 8) XX(N ## 9)
#define XXXX(N) \
    XXX(N ## 0) XXX(N ## 1) XXX(N ## 2) XXX(N ## 3) XXX(N ## 4) XXX(N ## 5)
XXX(N ## 6) XXX(N ## 7) XXX(N ## 8) XXX(N ## 9)
#define XXXXX(N) \
    XXXX(N ## 0) XXXX(N ## 1) XXXX(N ## 2) XXXX(N ## 3) XXXX(N ## 4) XXXX(N ##
5) XXXX(N ## 6) XXXX(N ## 7) XXXX(N ## 8) XXXX(N ## 9)
    XXXXX(1)
#if 0
    XXXXX(2)
    XXXXX(3)
    XXXXX(4)
    XXXXX(5)
    XXXXX(6)
    XXXXX(7)
    XXXXX(8)
    XXXXX(9)
#endif
    }
  return d;
}

I see SLSR taking all of the compile-time at -O1:

 straight-line strength reduction: 195.66 (95%) usr   0.02 ( 2%) sys 196.32
(94%) wall       0 kB ( 0%) ggc

something must go wrong here (testcase for a FRE change I am doing ...)