On 7/19/23 04:11, Xiao Zeng wrote:
This patch completes the recognition of the basic semantics
defined in the spec, namely:
Conditional zero, if condition is equal to zero
rd = (rs2 == 0) ? 0 : rs1
Conditional zero, if condition is non zero
rd = (rs2 != 0) ? 0 : rs1
gcc/ChangeLog:
* config/riscv/riscv.md: Include zicond.md
* config/riscv/zicond.md: New file.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zicond-primitiveSemantics.c: New test.
So I played with this a bit today. I originally thought that using
match_dup was the right way to go for those 4 secondary patterns. But
after further pondering it's not ideal.
match_dup will require pointer equality within the RTL structure. That
could inhibit detection in two cases. First, SUBREGs. SUBREGs are not
shared. So we'd never match if we had a SUBREG expression.
Second, post register allocation we can have the same looking RTX, but
it may not be pointer equal.
The SUBREG issue also means that we don't want to use a REGNO (x) ==
REGNO (y) style check because those macros are only valid on REG
expressions. We could strip the SUBREG, but that's usually awkward to
do in a pattern's condition.
The net result is we probably should use rtx_equal_p which I was hoping
to avoid. I'm testing with that change to the 4 secondary patterns
right now. Assuming that passes (and I have no reason to think it
won't) then I'll go ahead and commit #1 and #2 from this series which is
all I have time for today.
Jeff
