http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49429
--- Comment #9 from Easwaran Raman <eraman at google dot com> 2011-06-17
20:43:04 UTC ---
(In reply to comment #8)
> Compiling x.c with a ia64-unknown-linux cross compiler, setting a breakpoint
> in
> can_escape(), I see that,
>
>
> (gdb) p debug_rtx (body)
> (set (mem/s/c:DI (reg/f:DI 341) [2 s1+0 S8 A64])
> (reg:DI 112 in0))
>
> This is part of an instruction that gets removed:
> (insn 4 3 6 2 (set (mem/s/c:DI (reg/f:DI 341) [2 s1+0 S8 A64])
> (reg:DI 112 in0)) y.c:23 5 {movdi_internal}
> (expr_list:REG_DEAD (reg:DI 112 in0)
> (nil)))
>
> (gdb) p expr->base.code
> $24 = PARM_DECL
> (gdb) p may_be_aliased (expr)
> $23 = 0 '\000'
>
> So can_escape() returns false. But later on, in the same BB, I see:
>
>
> (insn 36 30 37 2 (set (reg:DI 120 out0)
> (reg/f:DI 357)) 5 {movdi_internal}
> (expr_list:REG_EQUAL (plus:DI (reg/f:DI 328 sfp)
> (const_int 62 [0x3e]))
> (nil)))
> (insn 37 36 38 2 (set (reg:DI 121 out1)
> (reg/f:DI 341)) 5 {movdi_internal}
> (expr_list:REG_DEAD (reg/f:DI 341)
> (expr_list:REG_EQUAL (plus:DI (reg/f:DI 328 sfp)
> (const_int 96 [0x60]))
> (nil))))
> (insn 38 37 39 2 (set (reg:DI 122 out2)
> (const_int 31 [0x1f])) 5 {movdi_internal}
> (nil))
> (call_insn 39 38 42 2 (parallel [
> (set (reg:DI 8 r8)
> (call (mem:DI (symbol_ref:DI ("memcpy") [flags 0x41]
> <function_decl 0x7ffff70d2e00 memcpy>) [0 memcpy S8 A64])
> (const_int 1 [0x1])))
> (clobber (reg:DI 320 b0))
> (clobber (scratch:DI))
> (clobber (scratch:DI))
> ]) 332 {call_value_gp}
> (expr_list:REG_DEAD (reg:DI 122 out2)
> (expr_list:REG_DEAD (reg:DI 121 out1)
> (expr_list:REG_DEAD (reg:DI 120 out0)
> (expr_list:REG_UNUSED (reg:DI 8 r8)
> (expr_list:REG_EH_REGION (const_int 0 [0])
> (nil))))))
> (expr_list:REG_DEP_TRUE (use (reg:DI 1 r1))
> (expr_list:REG_DEP_TRUE (use (reg:DI 122 out2))
> (expr_list:REG_DEP_TRUE (use (reg:DI 121 out1))
> (expr_list:REG_DEP_TRUE (use (reg:DI 120 out0))
> (nil))))))
>
> reg 341 is passed as source argument of a memcpy. Why does the expression
> return 0 for may_be_aliased()?
Could someone tell why may_be_aliased returns false in this case? I would
expect TREE_ADDRESSABLE to be true, but that's not the case. It seems to me
some other bug is exposed by the DSE patch.
