On 11/17/22 16:56, Palmer Dabbelt wrote:
On Thu, 17 Nov 2022 15:41:26 PST (-0800), gcc-patches@gcc.gnu.org wrote:
On 11/12/22 14:29, Philipp Tomsich wrote:
Users might use explicit arithmetic operations to create a mask and
then and it, in a sequence like
cond = (bits >> SHIFT) & 1;
mask = ~(cond - 1);
val &= mask;
which will present as a single-bit sign-extract.
Dependening on what combination of XVentanaCondOps and Zbs are
available, this will map to the following sequences:
- bexti + vt.maskc, if both Zbs and XVentanaCondOps are present
- andi + vt.maskc, if only XVentanaCondOps is available and the
sign-extract is operating on bits 10:0 (bit
11 can't be reached, as the immediate is
sign-extended)
- slli + srli + and, otherwise.
gcc/ChangeLog:
* config/riscv/xventanacondops.md: Recognize SIGN_EXTRACT
of a single-bit followed by AND for XVentanaCondOps.
Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
---
gcc/config/riscv/xventanacondops.md | 46
+++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
diff --git a/gcc/config/riscv/xventanacondops.md
b/gcc/config/riscv/xventanacondops.md
index 7930ef1d837..3e9d5833a4b 100644
--- a/gcc/config/riscv/xventanacondops.md
+++ b/gcc/config/riscv/xventanacondops.md
@@ -73,3 +73,49 @@
"TARGET_XVENTANACONDOPS"
[(set (match_dup 5) (match_dup 1))
(set (match_dup 0) (and:X (neg:X (ne:X (match_dup 5) (const_int
0)))
+
+;; Users might use explicit arithmetic operations to create a mask and
+;; then and it, in a sequence like
Nit. Seems like a word is missing. "make and then and it"??
Do we really care about TARGET_XVENTANACONDOPS && ! TARGET_ZBS?
I guess that's really more of a question for the Ventana folks, but
assuming all the Ventana widgets have Zbs then it seems reasonable to
just couple them -- there's already enough options in RISC-V land to
test everything, might as well make sure what slips through the cracks
isn't being built.
I'm pretty confident Ventana won't be making a part without Zbs which is
why I raised the issue
I also understand Philipp's position that one could explicitly turn on
ventanacondops and zbs off and that there's a notable possibility that
this ultimately turns into ZICondOps independent of Ventana.
So I guess we keep it... But it also feels like a ticking time bomb WRT
the ability to mix and match things the way we currently allow. I
suspect if we were to look at the full test matrix and deeply test that
full matrix that we'd find a number of problems where two options
interact badly.
Jeff
