[Bug rtl-optimization/49429] [4.7 Regression] dse.c changes to fix PR44194 (r175063) cause execution failures

[eraman at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49429

--- Comment #8 from Easwaran Raman <eraman at google dot com> 2011-06-16 
16:27:44 UTC ---
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()?