RISC-V: split to allow formation of sh[123]add before 32bit divw
When using strength-reduction, we will reduce a multiplication to a
sequence of shifts and adds. If this is performed with 32-bit types
and followed by a division, the lack of w-form sh[123]add will make
combination impossible and lead to a slli + addw being generated.
Split the sequence with the knowledge that a w-form div will perform
implicit sign-extensions.
gcc/ChangeLog:
* config/riscv/bitmanip.md: Add a define_split to optimize
slliw + addiw + divw into sh[123]add + divw.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zba-shNadd-05.c: New test.
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 2e7142c..73881a9 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -39,6 +39,23 @@
[(set_attr "type" "bitmanip")
(set_attr "mode" "<X:MODE>")])
+; When using strength-reduction, we will reduce a multiplication to a
+; sequence of shifts and adds. If this is performed with 32-bit types
+; and followed by a division, the lack of w-form sh[123]add will make
+; combination impossible and lead to a slli + addw being generated.
+; Split the sequence with the knowledge that a w-form div will perform
+; implicit sign-extensions.
+(define_split
+ [(set (match_operand:DI 0 "register_operand")
+ (sign_extend:DI (div:SI (plus:SI (subreg:SI (ashift:DI (match_operand:DI 1 "register_operand")
+ (match_operand:QI 2 "imm123_operand")) 0)
+ (subreg:SI (match_operand:DI 3 "register_operand") 0))
+ (subreg:SI (match_operand:DI 4 "register_operand") 0))))
+ (clobber (match_operand:DI 5 "register_operand"))]
+ "TARGET_64BIT && TARGET_ZBA"
+ [(set (match_dup 5) (plus:DI (ashift:DI (match_dup 1) (match_dup 2)) (match_dup 3)))
+ (set (match_dup 0) (sign_extend:DI (div:SI (subreg:SI (match_dup 5) 0) (subreg:SI (match_dup 4) 0))))])
+
(define_insn "*shNadduw"
[(set (match_operand:DI 0 "register_operand" "=r")
(plus:DI
diff --git a/gcc/testsuite/gcc.target/riscv/zba-shNadd-05.c b/gcc/testsuite/gcc.target/riscv/zba-shNadd-05.c
new file mode 100644
index 0000000..271c3a8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zba-shNadd-05.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zba -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-O1" "-Os" "-Oz" "-Og" } } */
+
+long long f(int a, int b)
+{
+ return (a * 3) / b;
+}
+
+/* { dg-final { scan-assembler-times "sh1add\t" 1 } } */
+/* { dg-final { scan-assembler-times "divw\t" 1 } } */
