Message ID | 20221108195456.2701279-1-philipp.tomsich@vrull.eu |
---|---|
State | New |
Headers | show |
Series | RISC-V: optimize '(a >= 0) ? b : 0' to srai + andn, if compiling for Zbb | expand |
On 11/8/22 12:54, Philipp Tomsich wrote: > If-conversion is turning '(a >= 0) ? b : 0' into a branchless sequence > not a5,a0 > srai a5,a5,63 > and a0,a1,a5 > missing the opportunity to combine the NOT and AND into an ANDN. > > This adds a define_split to help the combiner reassociate the NOT with > the AND. > > > gcc/ChangeLog: > > * config/riscv/bitmanip.md: New define_split. > > gcc/testsuite/ChangeLog: > > * gcc.target/riscv/zbb-srai-andn.c: New test. OK. FWIW, combine can be pretty sneaky in manipulating the result of a scc style insn. I've seen a port with pages and pages of special patterns to match what simplify_if_then_else would do. Jeff
Applied to master. Thanks! --Philipp. On Sun, 13 Nov 2022 at 01:24, Jeff Law <jeffreyalaw@gmail.com> wrote: > > > On 11/8/22 12:54, Philipp Tomsich wrote: > > If-conversion is turning '(a >= 0) ? b : 0' into a branchless sequence > > not a5,a0 > > srai a5,a5,63 > > and a0,a1,a5 > > missing the opportunity to combine the NOT and AND into an ANDN. > > > > This adds a define_split to help the combiner reassociate the NOT with > > the AND. > > > > > > gcc/ChangeLog: > > > > * config/riscv/bitmanip.md: New define_split. > > > > gcc/testsuite/ChangeLog: > > > > * gcc.target/riscv/zbb-srai-andn.c: New test. > > OK. > > > FWIW, combine can be pretty sneaky in manipulating the result of a scc > style insn. I've seen a port with pages and pages of special patterns > to match what simplify_if_then_else would do. > > > Jeff >
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md index b44fb9517e7..d26f3567182 100644 --- a/gcc/config/riscv/bitmanip.md +++ b/gcc/config/riscv/bitmanip.md @@ -128,6 +128,19 @@ [(set_attr "type" "bitmanip") (set_attr "mode" "<X:MODE>")]) +;; '(a >= 0) ? b : 0' is emitted branchless (from if-conversion). Without a +;; bit of extra help for combine (i.e., the below split), we end up emitting +;; not/srai/and instead of combining the not into an andn. +(define_split + [(set (match_operand:DI 0 "register_operand") + (and:DI (neg:DI (ge:DI (match_operand:DI 1 "register_operand") + (const_int 0))) + (match_operand:DI 2 "register_operand"))) + (clobber (match_operand:DI 3 "register_operand"))] + "TARGET_ZBB" + [(set (match_dup 3) (ashiftrt:DI (match_dup 1) (const_int 63))) + (set (match_dup 0) (and:DI (not:DI (match_dup 3)) (match_dup 2)))]) + (define_insn "*xor_not<mode>" [(set (match_operand:X 0 "register_operand" "=r") (not:X (xor:X (match_operand:X 1 "register_operand" "r") diff --git a/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c b/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c new file mode 100644 index 00000000000..afe9fba5f05 --- /dev/null +++ b/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c @@ -0,0 +1,15 @@ +/* { dg-do compile } */ +/* { dg-options "-march=rv64gc_zbb -mabi=lp64" } */ +/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-Os" "-Oz" } } */ + +long long foo0(long long a, long long b) +{ + if (a >= 0) + return b; + + return 0; +} + +/* { dg-final { scan-assembler-times "srai\t" 1 } } */ +/* { dg-final { scan-assembler-times "andn\t" 1 } } */ +