http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57281
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Target| |i?86-*-*
Status|ASSIGNED |NEW
Target Milestone|--- |4.9.0
Summary|x86_64-linux loop fails to |[4.9 Regression]
|terminate at -O3 -m32 |x86_64-linux loop fails to
| |terminate at -O3 -m32,
| |bogus extendsidi2_1
| |splitter
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
But the miscompile happens during RTL opts:
<bb 5>:
f.0_13 ={v} f;
*pretmp_4 = 0;
b.5_1 = b;
_23 = (long long int) b.5_1;
*pretmp_18 = _23;
*pretmp_4 = 0;
b.2_27 = b;
b.3_28 = b.2_27 + -1;
b = b.3_28;
if (b.3_28 != -20)
goto <bb 6>;
else
goto <bb 10>;
<bb 6>:
goto <bb 5>;
is ok, while
.L4:
movl f, %eax
movl f+4, %edx
movl $0, (%ecx)
movl b, %eax
movl %eax, (%ebx)
sarl $31, %eax
movl %eax, 4(%ebx)
subl $1, %eax
cmpl $-20, %eax
movl %eax, b
jne .L4
messes up the IV value - the store of the upper half of the long long
extended b into *pretmp_18 invalidates b (%eax) but that value is then
still used for the IV.
Ok pre-IRA/LRA:
(insn 19 18 20 4 (parallel [
(set (mem:DI (reg/f:SI 68 [ D.1736 ]) [4 *_18+0 S8 A64])
(sign_extend:DI (reg:SI 75 [ b ])))
(clobber (reg:CC 17 flags))
(clobber (scratch:SI))
]) t.c:9 137 {extendsidi2_1}
(expr_list:REG_DEAD (reg:SI 75 [ b ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
...
(insn 21 20 22 4 (set (reg:SI 76 [ b ])
(mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl 0x7fccdf73b098
b>) [2 b+0 S4 A32])) t.c:17 85 {*movsi_internal}
(nil))
(insn 22 21 23 4 (parallel [
(set (reg:SI 72 [ b.3 ])
(plus:SI (reg:SI 76 [ b ])
(const_int -1 [0xffffffffffffffff])))
(clobber (reg:CC 17 flags))
and after:
(insn 19 78 20 4 (parallel [
(set (mem:DI (reg/f:SI 3 bx [orig:68 D.1736 ] [68]) [4 *_18+0 S8
A64])
(sign_extend:DI (reg:SI 0 ax [orig:75 b ] [75])))
(clobber (reg:CC 17 flags))
(clobber (reg:SI 1 dx [80]))
]) t.c:9 137 {extendsidi2_1}
(expr_list:REG_UNUSED (reg:SI 1 dx [80])
(expr_list:REG_DEAD (reg:SI 0 ax [orig:75 b ] [75])
(nil))))
(insn 20 19 21 4 (set (mem:SI (reg/f:SI 2 cx [orig:61 D.1734 ] [61]) [2 *_4+0
S4 A32])
(const_int 0 [0])) t.c:21 85 {*movsi_internal}
(nil))
(note 21 20 80 4 NOTE_INSN_DELETED)
(insn 80 21 22 4 (set (reg:SI 0 ax [82])
(mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl 0x7fccdf73b098
b>) [2 b+0 S4 A32])) t.c:17 85 {*movsi_internal}
(nil))
and postreload optimizes it to
(insn 78 18 19 4 (set (reg:SI 0 ax [orig:75 b ] [75])
(mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl 0x7fccdf73b098
b>) [2 b+0 S4 A32])) t.c:9 85 {*movsi_internal}
(expr_list:REG_EQUIV (mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl
0x7fccdf73b098 b>) [2 b+0 S4 A32])
(nil)))
(insn 19 78 21 4 (parallel [
(set (mem:DI (reg/f:SI 3 bx [orig:68 D.1736 ] [68]) [4 *_18+0 S8
A64])
(sign_extend:DI (reg:SI 0 ax [orig:75 b ] [75])))
(clobber (reg:CC 17 flags))
(clobber (reg:SI 1 dx [80]))
]) t.c:9 137 {extendsidi2_1}
(expr_list:REG_UNUSED (reg:SI 1 dx [80])
(expr_list:REG_DEAD (reg:SI 0 ax [orig:75 b ] [75])
(nil))))
(note 21 19 80 4 NOTE_INSN_DELETED)
(insn 80 21 22 4 (set (reg:SI 0 ax [82])
(reg:SI 0 ax [orig:75 b ] [75])) t.c:17 85 {*movsi_internal}
(nil))
(insn 22 80 23 4 (parallel [
(set (reg:SI 0 ax [orig:72 b.3 ] [72])
(plus:SI (reg:SI 0 ax [82])
(const_int -1 [0xffffffffffffffff])))
(clobber (reg:CC 17 flags))
but broken by split, which clobbers ax:
(insn 78 18 89 4 (set (reg:SI 0 ax [orig:75 b ] [75])
(mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl 0x7fccdf73b098
b>) [2 b+0 S4 A32])) t.c:9 85 {*movsi_internal}
(expr_list:REG_EQUIV (mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl
0x7fccdf73b098 b>) [2 b+0 S4 A32])
(nil)))
(insn 89 78 90 4 (set (mem:SI (reg/f:SI 3 bx [orig:68 D.1736 ] [68]) [4 *_18+0
S4 A64])
(reg:SI 0 ax [orig:75 b ] [75])) t.c:9 85 {*movsi_internal}
(nil))
(insn 90 89 91 4 (parallel [
(set (reg:SI 0 ax [orig:75 b ] [75])
(ashiftrt:SI (reg:SI 0 ax [orig:75 b ] [75])
(const_int 31 [0x1f])))
(clobber (reg:CC 17 flags))
]) t.c:9 529 {ashrsi3_cvt}
(nil))
(insn 91 90 21 4 (set (mem:SI (plus:SI (reg/f:SI 3 bx [orig:68 D.1736 ] [68])
(const_int 4 [0x4])) [4 *_18+4 S4 A32])
(reg:SI 0 ax [orig:75 b ] [75])) t.c:9 85 {*movsi_internal}
(nil))
(note 21 91 22 4 NOTE_INSN_DELETED)
(insn 22 21 23 4 (parallel [
(set (reg:SI 0 ax [orig:72 b.3 ] [72])
(plus:SI (reg:SI 0 ax [82])
(const_int -1 [0xffffffffffffffff])))
(clobber (reg:CC 17 flags))
]) t.c:17 260 {*addsi_1}
(expr_list:REG_DEAD (reg:SI 0 ax [82])
(expr_list:REG_EQUAL (plus:SI (mem/c:SI (symbol_ref:SI ("b") [flags
0x2] <var_decl 0x7fccdf73b098 b>) [2 b+0 S4 A32])
(const_int -1 [0xffffffffffffffff]))
(nil))))
(insn 23 22 24 4 (set (mem/c:SI (symbol_ref:SI ("b") [flags 0x2] <var_decl
0x7fccdf73b098 b>) [2 b+0 S4 A32])
(reg:SI 0 ax [orig:72 b.3 ] [72])) t.c:17 85 {*movsi_internal}
(nil))
