Message ID | 20221108195547.2701347-1-philipp.tomsich@vrull.eu |
---|---|
State | New |
Headers | show |
Series | RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1" | expand |
On 11/8/22 12:55, Philipp Tomsich wrote: > Consider creating a polarity-reversed mask from a set-bit (i.e., if > the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb, > this can be expressed as bexti, followed by an addi of minus-one. To > enable the combiner to discover this opportunity, we need to split the > canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form > combinable into bexti. > > Consider the function: > long f(long a) > { > return (a & (1 << BIT_NO)) ? 0 : -1; > } > This produces the following sequence prior to this change: > andi a0,a0,16 > seqz a0,a0 > neg a0,a0 > ret > Following this change, it results in: > bexti a0,a0,4 > addi a0,a0,-1 > ret > > gcc/ChangeLog: > > * config/riscv/bitmanip.md: Add a splitter to generate > polarity-reversed masks from a set bit using bexti + addi. > > gcc/testsuite/ChangeLog: > > * gcc.target/riscv/zbs-bexti.c: New test. OK Jeff
Committed to master. Thanks! Philipp. On Thu, 17 Nov 2022 at 15:43, Jeff Law <jeffreyalaw@gmail.com> wrote: > > > On 11/8/22 12:55, Philipp Tomsich wrote: > > Consider creating a polarity-reversed mask from a set-bit (i.e., if > > the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb, > > this can be expressed as bexti, followed by an addi of minus-one. To > > enable the combiner to discover this opportunity, we need to split the > > canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form > > combinable into bexti. > > > > Consider the function: > > long f(long a) > > { > > return (a & (1 << BIT_NO)) ? 0 : -1; > > } > > This produces the following sequence prior to this change: > > andi a0,a0,16 > > seqz a0,a0 > > neg a0,a0 > > ret > > Following this change, it results in: > > bexti a0,a0,4 > > addi a0,a0,-1 > > ret > > > > gcc/ChangeLog: > > > > * config/riscv/bitmanip.md: Add a splitter to generate > > polarity-reversed masks from a set bit using bexti + addi. > > > > gcc/testsuite/ChangeLog: > > > > * gcc.target/riscv/zbs-bexti.c: New test. > > OK > > > Jeff > >
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md index d26f3567182..30dabdf8ddc 100644 --- a/gcc/config/riscv/bitmanip.md +++ b/gcc/config/riscv/bitmanip.md @@ -394,3 +394,16 @@ "TARGET_ZBS && UINTVAL (operands[2]) < GET_MODE_BITSIZE (<MODE>mode)" "bexti\t%0,%1,%2" [(set_attr "type" "bitmanip")]) + +;; We can create a polarity-reversed mask (i.e. bit N -> { set = 0, clear = -1 }) +;; using a bext(i) followed by an addi instruction. +;; This splits the canonical representation of "(a & (1 << BIT_NO)) ? 0 : -1". +(define_split + [(set (match_operand:GPR 0 "register_operand") + (neg:GPR (eq:GPR (zero_extract:GPR (match_operand:GPR 1 "register_operand") + (const_int 1) + (match_operand 2)) + (const_int 0))))] + "TARGET_ZBS" + [(set (match_dup 0) (zero_extract:GPR (match_dup 1) (const_int 1) (match_dup 2))) + (set (match_dup 0) (plus:GPR (match_dup 0) (const_int -1)))]) diff --git a/gcc/testsuite/gcc.target/riscv/zbs-bexti.c b/gcc/testsuite/gcc.target/riscv/zbs-bexti.c new file mode 100644 index 00000000000..99e3b58309c --- /dev/null +++ b/gcc/testsuite/gcc.target/riscv/zbs-bexti.c @@ -0,0 +1,14 @@ +/* { dg-do compile } */ +/* { dg-options "-march=rv64gc_zbs -mabi=lp64 -O2" } */ + +/* bexti */ +#define BIT_NO 4 + +long +foo0 (long a) +{ + return (a & (1 << BIT_NO)) ? 0 : -1; +} + +/* { dg-final { scan-assembler "bexti" } } */ +/* { dg-final { scan-assembler "addi" } } */