https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78794
--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Uroš Bizjak from comment #7)
> Yes, this is a good idea.
Also, since pandn on non-BMI target replaces four arith insns with one, the
gain should be raised for 2 * ix86_cost->add for a total of 3 * ix86_cost->add.
The final patch is thus:
--cut here--
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 1cd1cd8..6a746b2 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -3417,7 +3417,11 @@ dimode_scalar_chain::compute_convert_gain ()
|| GET_CODE (src) == AND)
{
gain += ix86_cost->add;
- if (CONST_INT_P (XEXP (src, 0)))
+ /* Additional gain for andnot for targets without BMI. */
+ if (GET_CODE (XEXP (src, 0)) == NOT
+ && !TARGET_BMI)
+ gain += 2 * ix86_cost->add;
+ else if (CONST_INT_P (XEXP (src, 0)))
gain -= vector_const_cost (XEXP (src, 0));
if (CONST_INT_P (XEXP (src, 1)))
gain -= vector_const_cost (XEXP (src, 1));
--cut here-
Please also note that on BMI targets, the attached testcase won't be converted,
which is a good thing - the loop on BMI targets looks like:
.L4:
movl 4(%eax), %edi
andn 4(%esp), %edi, %ebx
movl (%eax), %esi
movl %ebx, %ebp
andn (%esp), %esi, %ecx
orl %ecx, %ebp
jne .L3
xorl 8(%esp), %esi
xorl 12(%esp), %edi
movl %esi, (%eax)
movl %edi, 4(%eax)
.L3:
addl $12, %eax
cmpl %edx, %eax
jne .L4
