------- Comment #5 from ubizjak at gmail dot com 2007-07-01 09:33 -------
Confirmed. This is the same bug as PR32533, but this one comes with the c
testcase. The problem is in ifcvt pass.
In -march=nocona case (-march=nocona -O2 -ftree-vectorize), we have following
code before ifcvt pass:
if (high_top_bit_11 != 0)
goto <bb 5>;
else
goto <bb 4>;
<bb 4>:
if (d_7(D) <= high_19)
goto <bb 5>;
else
goto <bb 6>;
<bb 5>:
high_21 = high_19 - d_7(D);
quotient_22 = quotient_20 | 1;
<bb 6>:
# quotient_3 = PHI <quotient_20(4), quotient_22(5)>
# high_1 = PHI <high_19(4), high_21(5)>
j_23 = j_32 + 1;
This code is converted by ifcvt pass to:
quotient_20 = quotient_31 << 1; [+]
D.2068_5 = high_top_bit_11 == 0;
D.2069_4 = d_7(D) <= high_19;
_ifc_.29_2 = D.2068_5 && D.2069_4;
D.2071_29 = high_top_bit_11 == 0;
D.2072_33 = d_7(D) > high_19;
_ifc_.30_34 = D.2071_29 && D.2072_33;
high_21 = high_19 - d_7(D);
quotient_22 = quotient_20 | 1; [++]
quotient_3 = high_top_bit_11 == 0 ? quotient_20 : quotient_22; <<< here!
high_1 = high_top_bit_11 == 0 ? high_19 : high_21; <<< here!
j_23 = j_32 + 1;
The condition for quotient_3 [and high_1], produced by ifcvt pass is wrong, and
should be:
quotient_3 = _ifc_.3034 ? quotient_20 : quotient_22;
This is evident from the inner loop of the testcase:
--cut here--
{
word high_top_bit = (high & MP_WORD_TOP_BIT);
high <<= 1;
high |= (n0 >> (MP_WORD_BITS-1-j)) & 1;
quotient <<= 1; [+]
if(high_top_bit || high >= d) <<<< _the_condition_
{
high -= d;
quotient |= 1; [++]
}
}
--cut here--
Due to slighlty different gimple generation for -march=core2 (please look into
_.004t.gimple) where only if branch is created, ifcvt is able to create correct
code:
quotient_20 = quotient_34 << 1; [+]
D.2065_21 = high_top_bit_11 != 0;
D.2066_22 = high_19 >= d_7(D);
D.2067_23 = D.2065_21 || D.2066_22;
high_24 = high_19 - d_7(D);
quotient_25 = quotient_20 | 1; [++]
quotient_3 = D.2067_23 ? quotient_25 : quotient_20; <<<< here
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ubizjak at gmail dot com
Priority|P3 |P1
Summary|Miscompiles valid code with |[4.1/4.2/4.3 Regression]
|-ftree-vectorize and - |Miscompiles valid code with
|march=nocona |-ftree-vectorize
Target Milestone|--- |4.1.3
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31966
