From 065be0ffbcd676b635d492f4679e635b6ece4fe4 Mon Sep 17 00:00:00 2001
From: Matevos Mehrabyan <matevosmehrabyan@gmail.com>
Date: Fri, 28 Apr 2023 14:01:30 -0600
Subject: [PATCH] RISC-V: Add divmod expansion support
Hi all,
If we have division and remainder calculations with the same operands:
a = b / c;
d = b % c;
We can replace the calculation of remainder with multiplication +
subtraction, using the result from the previous division:
a = b / c;
d = a * c;
d = b - d;
Which will be faster.
Currently, it isn't done for RISC-V.
I've added an expander for DIVMOD which replaces 'rem' with 'mul + sub'.
Best regards,
Matevos.
gcc/ChangeLog:
* config/riscv/iterators.md (only_div, paired_mod): New iterators.
(u): Add div/udiv cases.
* config/riscv/riscv-protos.h (riscv_use_divmod_expander): Prototype.
* config/riscv/riscv.cc (struct riscv_tune_param): Add field for
divmod expansion.
(rocket_tune_info, sifive_7_tune_info): Initialize new field.
(thead_c906_tune_info): Likewise.
(optimize_size_tune_info): Likewise.
(riscv_use_divmod_expander): New function.
* config/riscv/riscv.md (<u>divmod<mode>4): New expander.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/divmod-1.c: New testcase.
* gcc.target/riscv/divmod-2.c: New testcase.
---
gcc/config/riscv/iterators.md | 6 ++++++
gcc/config/riscv/riscv-protos.h | 1 +
gcc/config/riscv/riscv.cc | 15 +++++++++++++++
gcc/config/riscv/riscv.md | 16 ++++++++++++++++
gcc/testsuite/gcc.target/riscv/divmod-1.c | 11 +++++++++++
gcc/testsuite/gcc.target/riscv/divmod-2.c | 16 ++++++++++++++++
6 files changed, 65 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/riscv/divmod-1.c
create mode 100644 gcc/testsuite/gcc.target/riscv/divmod-2.c
diff --git a/gcc/config/riscv/iterators.md b/gcc/config/riscv/iterators.md
index 9b7670384523..1d56324df03a 100644
--- a/gcc/config/riscv/iterators.md
+++ b/gcc/config/riscv/iterators.md
@@ -152,6 +152,11 @@
;; from the same template.
(define_code_iterator any_mod [mod umod])
+;; These code iterators allow unsigned and signed divmod to be generated
+;; from the same template.
+(define_code_iterator only_div [div udiv])
+(define_code_attr paired_mod [(div "mod") (udiv "umod")])
+
;; These code iterators allow the signed and unsigned scc operations to use
;; the same template.
(define_code_iterator any_gt [gt gtu])
@@ -181,6 +186,7 @@
(lt "") (ltu "u")
(le "") (leu "u")
(fix "") (unsigned_fix "u")
+ (div "") (udiv "u")
(float "") (unsigned_float "u")])
;; <su> is like <u>, but the signed form expands to "s" rather than "".
diff --git a/gcc/config/riscv/riscv-protos.h b/gcc/config/riscv/riscv-protos.h
index f87661bde2cf..5a927bdf1b06 100644
--- a/gcc/config/riscv/riscv-protos.h
+++ b/gcc/config/riscv/riscv-protos.h
@@ -239,4 +239,5 @@ extern const char*
th_mempair_output_move (rtx[4], bool, machine_mode, RTX_CODE);
#endif
+extern bool riscv_use_divmod_expander (void);
#endif /* ! GCC_RISCV_PROTOS_H */
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 1529855a2b4c..09a30dc260fc 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -236,6 +236,7 @@ struct riscv_tune_param
unsigned short memory_cost;
unsigned short fmv_cost;
bool slow_unaligned_access;
+ bool use_divmod_expansion;
};
/* Information about one micro-arch we know about. */
@@ -323,6 +324,7 @@ static const struct riscv_tune_param rocket_tune_info = {
5, /* memory_cost */
8, /* fmv_cost */
true, /* slow_unaligned_access */
+ false, /* use_divmod_expansion */
};
/* Costs to use when optimizing for Sifive 7 Series. */
@@ -337,6 +339,7 @@ static const struct riscv_tune_param sifive_7_tune_info = {
3, /* memory_cost */
8, /* fmv_cost */
true, /* slow_unaligned_access */
+ false, /* use_divmod_expansion */
};
/* Costs to use when optimizing for T-HEAD c906. */
@@ -351,6 +354,7 @@ static const struct riscv_tune_param thead_c906_tune_info = {
5, /* memory_cost */
8, /* fmv_cost */
false, /* slow_unaligned_access */
+ false /* use_divmod_expansion */
};
/* Costs to use when optimizing for size. */
@@ -365,6 +369,7 @@ static const struct riscv_tune_param optimize_size_tune_info = {
2, /* memory_cost */
8, /* fmv_cost */
false, /* slow_unaligned_access */
+ false, /* use_divmod_expansion */
};
static tree riscv_handle_fndecl_attribute (tree *, tree, tree, int, bool *);
@@ -7210,6 +7215,16 @@ riscv_lshift_subword (machine_mode mode, rtx value, rtx shift,
gen_lowpart (QImode, shift)));
}
+/* Return TRUE if we should use the divmod expander, FALSE otherwise. This
+ allows the behavior to be tuned for specific implementations as well as
+ when optimizing for size. */
+
+bool
+riscv_use_divmod_expander (void)
+{
+ return tune_param->use_divmod_expansion;
+}
+
/* Initialize the GCC target structure. */
#undef TARGET_ASM_ALIGNED_HI_OP
#define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 376a8831820e..c508ee3ad89f 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -1063,6 +1063,22 @@
[(set_attr "type" "idiv")
(set_attr "mode" "DI")])
+(define_expand "<u>divmod<mode>4"
+ [(parallel
+ [(set (match_operand:GPR 0 "register_operand")
+ (only_div:GPR (match_operand:GPR 1 "register_operand")
+ (match_operand:GPR 2 "register_operand")))
+ (set (match_operand:GPR 3 "register_operand")
+ (<paired_mod>:GPR (match_dup 1) (match_dup 2)))])]
+ "TARGET_DIV && riscv_use_divmod_expander ()"
+ {
+ rtx tmp = gen_reg_rtx (<MODE>mode);
+ emit_insn (gen_<u>div<GPR:mode>3 (operands[0], operands[1], operands[2]));
+ emit_insn (gen_mul<GPR:mode>3 (tmp, operands[0], operands[2]));
+ emit_insn (gen_sub<GPR:mode>3 (operands[3], operands[1], tmp));
+ DONE;
+ })
+
(define_insn "*<optab>si3_extended"
[(set (match_operand:DI 0 "register_operand" "=r")
(sign_extend:DI
diff --git a/gcc/testsuite/gcc.target/riscv/divmod-1.c b/gcc/testsuite/gcc.target/riscv/divmod-1.c
new file mode 100644
index 000000000000..9706611b500c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/divmod-1.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+
+void
+foo(int a, int b, int *c, int *d)
+{
+ *c = a / b;
+ *d = a % b;
+}
+
+/* { dg-final { scan-assembler-times "\tdiv" 1 } } */
+/* { dg-final { scan-assembler-times "\trem" 1} } */
diff --git a/gcc/testsuite/gcc.target/riscv/divmod-2.c b/gcc/testsuite/gcc.target/riscv/divmod-2.c
new file mode 100644
index 000000000000..dfd319e52c01
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/divmod-2.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* Skip this everywhere for now. Once we have a target with
+ divmod enabled, only skip for -O0, -O1, -Og, -Oz, -Os. */
+/* { dg-skip-if "" { *-*-* } { } } */
+
+void
+foo(int a, int b, int *c, int *d)
+{
+ *c = a / b;
+ *d = a % b;
+}
+
+/* { dg-final { scan-assembler-not "\trem" } } */
+/* { dg-final { scan-assembler-times "\tdiv" 1 } } */
+/* { dg-final { scan-assembler-times "\tmul" 1 } } */
+/* { dg-final { scan-assembler-times "\tsub" 1 } } */
--
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