[Bug tree-optimization/45256] New: Missed arithmetic simplification at tree level

[bernds at gcc dot gnu dot org]

I'll attach a testcase, which shows a missed simplification at tree level:

  D.2276_42 = i_53 + 1;
  D.2277_43 = D.2276_42 * 32;
  iftmp.3_55 = __fswab32 (xb_54);
  __asm__("clz  %0, %1" : "=r" ret_56 : "r" iftmp.3_55 : "cc");
  ret_58 = 32 - ret_56;
  ret_59 = D.2277_43 - ret_58;

In effect, the constant 32 is both added and subtracted from the result.  With
a four-insn combiner, this is caught at the RTL stage (compiling for Thumb-1):

-       add     r2, r2, #1
        lsl     r2, r2, #5
-       add     r3, r3, r2
-       sub     r3, r3, #32
+       add     r3, r2, r3


-- 
           Summary: Missed arithmetic simplification at tree level
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bernds at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: arm-none-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45256