From 1957bedf29a1b2cc231972aba680fe80199d5498 Mon Sep 17 00:00:00 2001 From: Philipp Tomsich Date: Tue, 9 Nov 2021 18:54:54 +0100 Subject: [PATCH] RISC-V: bitmanip: add splitter to use bexti for "(a & (1 << BIT_NO)) ? 0 : -1" 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. --- gcc/config/riscv/bitmanip.md | 13 +++++++++++++ gcc/testsuite/gcc.target/riscv/zbs-bexti.c | 2 +- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md index fb062f6..0dd6ebb 100644 --- a/gcc/config/riscv/bitmanip.md +++ b/gcc/config/riscv/bitmanip.md @@ -429,3 +429,16 @@ (const_int 1) (match_dup 2))) (set (match_dup 0) (xor:X (match_dup 0) (const_int 1)))]) + +;; 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 index c15098e..d7a8963 100644 --- a/gcc/testsuite/gcc.target/riscv/zbs-bexti.c +++ b/gcc/testsuite/gcc.target/riscv/zbs-bexti.c @@ -26,6 +26,6 @@ long bexti64_4(long a, char bitno) } /* { dg-final { scan-assembler-times "bexti\t" 4 } } */ -/* { dg-final { scan-assembler-times "xori\t|snez\t" 1 } } */ +/* { dg-final { scan-assembler-times "xori\t" 1 } } */ /* { dg-final { scan-assembler-times "addi\t" 1 } } */ /* { dg-final { scan-assembler-times "neg\t" 1 } } */ -- 2.7.4