Hi
This patch add support for the missing transformation of (x | y) == x ->
(y & ~x) == 0.
The transformation for (x & y) == x case already exists in
simplify-rtx.c since 2014 as of r218503 and this patch only adds a
couple of extra patterns for the IOR case.
Citing the example given in PR82439 :
Simple testcase (f1 should generate the same as f2):
int f1(int x, int y) { return (x | y) == x; }
int f2(int x, int y) { return (y & ~x) == 0; }
f1:
orr w1, w0, w1
cmp w1, w0
cset w0, eq
ret
f2:
bics wzr, w1, w0
cset w0, eq
ret
This benefits targets that have the BICS instruction to generate better
code. Wilco helped me in showing that even in targets that do not have
the BICS instruction, this is no worse and gives out 2 instructions.
For example in x86:
0000000000000000 <f1>:
0: 09 fe or %edi,%esi
2: 31 c0 xor %eax,%eax
4: 39 fe cmp %edi,%esi
6: 0f 94 c0 sete %al
9: c3 retq
0000000000000010 <f2>:
10: f7 d7 not %edi
12: 31 c0 xor %eax,%eax
14: 85 f7 test %esi,%edi
16: 0f 94 c0 sete %al
19: c3 retq
Testing done: Checked for regressions on bootstrapped
aarch64-none-linux-gnu and arm-none-linux-gnueabihf and added new test
cases.
Is this ok for trunk?
Sudi
ChangeLog Entries:
*** gcc/ChangeLog ***
2017-01-03 Sudakshina Das <sudi....@arm.com>
PR target/82439
* simplify-rtx.c (simplify_relational_operation_1): Add
simplifications of (x|y) == x for BICS pattern.
*** gcc/testsuite/ChangeLog ***
2017-01-03 Sudakshina Das <sudi....@arm.com>
PR target/82439
* gcc.target/aarch64/bics_5.c: New test.
* gcc.target/arm/bics_5.c: Likewise.
