PR rtl-optimization/96692: ((A|B)^C)^A using andn with -mbmi on x86.
This patch addresses PR rtl-optimization/96692 on x86_64, by providing
a set of combine splitters to convert the three operation ((A|B)^C)^D
into a two operation sequence using andn when either A or B is the same
register as C or D. This is essentially a reassociation problem that's
only a win if the target supports an and-not instruction (as with -mbmi).
Hence for the new test case:
int f(int a, int b, int c)
return (a ^ b) ^ (a | c);
GCC on x86_64-pc-linux-gnu wth -O2 -mbmi would previously generate:
xorl %edi, %esi
orl %edx, %edi
movl %esi, %eax
xorl %edi, %eax
but with this patch now generates:
andn %edx, %edi, %eax
xorl %esi, %eax
2022-07-05 Roger Sayle <firstname.lastname@example.org>
Uroš Bizjak <email@example.com>
* config/i386/i386.md (define_split): Split ((A | B) ^ C) ^ D
as (X & ~Y) ^ Z on target BMI when either C or D is A or B.
* gcc.target/i386/bmi-andn-4.c: New test case.
2 files changed