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| author | Philipp Tomsich <philipp.tomsich@vrull.eu> | 2022-09-23 01:37:14 +0200 |
|---|---|---|
| committer | Philipp Tomsich <philipp.tomsich@vrull.eu> | 2022-11-13 16:47:20 +0100 |
| commit | 43435c7eb0ff60f02838674efd99df93852a92cc (patch) | |
| tree | e2d0410750a24131f53df90d45047a871a7e1216 | |
| parent | 3bf46ea7bce58918ae8da1c936fe4c55456d2b6b (diff) | |
| download | gcc-43435c7eb0ff60f02838674efd99df93852a92cc.zip gcc-43435c7eb0ff60f02838674efd99df93852a92cc.tar.gz gcc-43435c7eb0ff60f02838674efd99df93852a92cc.tar.bz2 | |
RISC-V: optimize '(a >= 0) ? b : 0' to srai + andn, if compiling for Zbb
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.
| -rw-r--r-- | gcc/config/riscv/bitmanip.md | 13 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c | 15 |
2 files changed, 28 insertions, 0 deletions
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md index b44fb95..d26f356 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 0000000..afe9fba --- /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 } } */ + |