[Bug tree-optimization/33498] [4.2/4.3 Regression] Optimizer (-O2) may convert a normal loop to infinite

["rask at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from rask at gcc dot gnu dot org  2007-09-19 16:12 -------
Technically, the code is undefined (overflow of signed integer val). Using -O2
-fno-strict-overflow results in a loop test, but the code looks dubious:

table_init:
        pushl   %ebp    # 51    *pushsi2        [length = 1]
        movl    $117835012, %eax        # 20    *movsi_1/1      [length = 5]
        movl    %esp, %ebp      # 52    *movsi_1/1      [length = 2]
        movl    $2, %edx        # 21    *movsi_1/1      [length = 5]
        movl    8(%ebp), %ecx   # 14    *movsi_1/1      [length = 3]
        movl    $50462976, (%ecx)       # 19    *movsi_1/2      [length = 6]
        .p2align 4,,7
.L2:
        movl    %eax, -4(%ecx,%edx,4)   # 24    *movsi_1/2      [length = 4]
        addl    $67372036, %eax # 26    *addsi_1/1      [length = 6]
        addl    $1, %edx        # 27    *addsi_1/1      [length = 3]
        cmpl    $67305984, %eax # 29    *cmpsi_1_insn/1 [length = 6]
        jne     .L2     # 30    *jcc_1  [length = 2]
        popl    %ebp    # 55    popsi1  [length = 1]
        ret     # 56    return_internal [length = 1]

 -O2 -fno-tree-loop-optimize produces code which looks like it might even loop
the intended number of times:

table_init:
        pushl   %ebp    # 43    *pushsi2        [length = 1]
        movl    $1, %eax        # 12    *movsi_1/1      [length = 5]
        movl    %esp, %ebp      # 44    *movsi_1/1      [length = 2]
        movl    $117835012, %edx        # 13    *movsi_1/1      [length = 5]
        movl    8(%ebp), %ecx   # 6     *movsi_1/1      [length = 3]
        movl    $50462976, (%ecx)       # 11    *movsi_1/2      [length = 6]
        .p2align 4,,7
.L2:
        movl    %edx, (%ecx,%eax,4)     # 16    *movsi_1/2      [length = 3]
        addl    $1, %eax        # 20    *addsi_1/1      [length = 3]
        addl    $67372036, %edx # 18    *addsi_1/1      [length = 6]
        cmpl    $63, %eax       # 21    *cmpsi_1_insn/1 [length = 3]
        jle     .L2     # 22    *jcc_1  [length = 2]
        popl    %ebp    # 47    popsi1  [length = 1]
        ret     # 48    return_internal [length = 1]


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33498