On 9/4/26 5:27 AM, Jakub Jelinek wrote:
Hi!
The following patch attempts to improve code generation for
__builtin_bitreverse{8,16,32,64} when ZBKB extension is enabled, by using
brev8 a0,a0
or
rev8 a0,a0
brev8 t0,a0
srli a0,t0,48 ! 16 for rv32
or (bitreversesi2 if rv64)
rev8 a0,a0
brev8 t0,a0
srai a0,t0,32
or (bitreversesi2 if rv32 or bitreversedi2 if rv64)
rev8 a0,a0
brev8 a0,a0
Only tested in a cross on a testcase with the 4 builtins, hope CI will pick
this up when posted with RISC-V in the subject.
The bswaphi2 change is not strictly necessary, just weird to limit it
only to TARGET_ZBB when bswap<word_mode>2 is also TARGET_ZBKB.
2026-09-04 Jakub Jelinek <[email protected]>
PR target/126671
* config/riscv/bitmanip.md (bswaphi2): Use
TARGET_ZBB || TARGET_ZBKB condition instead of just
TARGET_ZBB.
(bitreverse<mode>2): New expander.
I'm not aware of a design in the wild supporting Zbkb, I've tried a
couple times to get that added to our supported set without success
(mostly I want the pack family of instructions).
--- a/gcc/config/riscv/bitmanip.md 2026-08-31 17:12:13.964850866 +0200
+++ b/gcc/config/riscv/bitmanip.md 2026-09-04 12:36:05.599948978 +0200
@@ -549,7 +549,7 @@ (define_insn "*bswap<mode>2"
(define_expand "bswaphi2"
[(set (match_operand:HI 0 "register_operand" "=r")
(bswap:HI (match_operand:HI 1 "register_operand" "r")))]
- "TARGET_ZBB"
+ "TARGET_ZBB || TARGET_ZBKB"
Trivially OK. If you find others, feel free to just fix them. Zbkb
always implies Zbb.
{
rtx tmp = gen_reg_rtx (word_mode);
rtx newop1 = gen_lowpart (word_mode, operands[1]);
@@ -566,6 +566,41 @@ (define_expand "bswaphi2"
DONE;
})
+(define_expand "bitreverse<mode>2"
+ [(match_operand:ANYI 0 "register_operand")
+ (match_operand:ANYI 1 "register_operand")]
+ "TARGET_ZBKB"
I'd be a lot more comfortable with a test in the testsuite that at least
verified the code generation via scan-asm or check-function-bodies. If
you look at crc-22-zbkb, I think it has the magic necessary to have a
run test which could be run on a suitable design or in QEMU.
jeff
