On 2/10/23 15:41, Philipp Tomsich wrote:
When if-conversion encounters sequences using immediates, the
sequences can't trivially map back onto czero.eqz/czero.nezt (even if
benefitial) due to czero.eqz/czero.nez not having immediate forms.
This adds a splitter to rewrite opportunities for Zicond that operate
on an immediate by first putting the immediate into a register to
enable the non-immediate czero.eqz/czero.nez instructions to operate
on the value.
Consider code, such as
long func2 (long a, long c)
{
if (c)
a = 2;
else
a = 5;
return a;
}
which will be converted to
func2:
seqz a0,a2
neg a0,a0
andi a0,a0,3
addi a0,a0,2
ret
Following this change, we generate
li a0,3
czero.nez a0,a0,a2
addi a0,a0,2
ret
This commit also introduces a simple unit test for if-conversion with
immediate (literal) values as the sources for simple sets in the THEN
and ELSE blocks. The test checks that the conditional-zero instruction
(czero.eqz/nez) is emitted as part of the resulting branchless
instruction sequence.
gcc/ChangeLog:
* config/riscv/zicond.md: Support immediates for
czero.eqz/czero.nez through a splitter.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zicond-ifconv-imm.c: New test.
Same comment & resolution as with the #3 in this series.
A note though. I've got Raphael looking at wiring this capability into
the mov<mode>cc expander as well. When complete that *may* make this
patch largely obsolete. But I don't think we necessarily need to wait
for that to work to land this patch.
jeff
