[Bug rtl-optimization/23376] ICE on GCC 4.x with -O1 -funroll-loops -fvariable-expansion-in-unroller

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-08-14 
11:36 -------
GCC tries to unroll and expand this insn: 
(insn 28 26 30 2 (set (reg/v:V2SI 65 [ sum ]) 
        (plus:V2SI (reg/v:V2SI 65 [ sum ]) 
            (reg/v:V2SI 68 [ ref1 ]))) 1023 {mmx_addv2si3} (nil) 
    (nil)) 
 
But for some reason the force_operand call in combine_var_copies_in_loop_exit 
returns NULL, in other words it fails to synthesize this insn in the unrolled 
copies.  At that point we have: 
 
2088      expr = force_operand (sum, ve->reg); 
(gdb) p debug_rtx(ve->insn) 
(insn 28 26 30 2 (set (reg/v:V2SI 65 [ sum ]) 
        (plus:V2SI (reg/v:V2SI 65 [ sum ]) 
            (reg/v:V2SI 68 [ ref1 ]))) -1 (nil) 
    (nil)) 
$42 = void 
(gdb) p debug_rtx(ve->reg) 
(reg/v:V2SI 65 [ sum ]) 
$43 = void 
(gdb) p debug_rtx(sum) 
(plus:V2SI (reg:V2SI 76) 
    (reg/v:V2SI 65 [ sum ])) 
$44 = void 
(gdb) 
2089      if (expr != ve->reg) 
(gdb) p expr 
$45 = 0x0 
(gdb)  
 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23376