[PATCH] RISC-V: Produce better code with complex constants [PR95632] [PR106602]

[Raphael Moreira Zinsly <rzinsly@ventanamicro.com>]

Due to RISC-V limitations on operations with big constants combine
is failing to match such operations and is not being able to
produce optimal code as it keeps splitting them. By pretending we
can do those operations we can get more opportunities for
simplification of surrounding instructions.

2022-12-06 Raphael Moreira Zinsly <rzinsly@ventanamicro.com>
           Jeff Law <jlaw@ventanamicro.com>

gcc/Changelog:
	PR target/95632
        PR target/106602
        * config/riscv/riscv.md: New pattern to simulate complex
        const_int loads.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/pr95632.c: New test.
        * gcc.target/riscv/pr106602.c: Likewise.
---
 gcc/config/riscv/riscv.md                 | 16 ++++++++++++++++
 gcc/testsuite/gcc.target/riscv/pr106602.c | 14 ++++++++++++++
 gcc/testsuite/gcc.target/riscv/pr95632.c  | 15 +++++++++++++++
 3 files changed, 45 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/riscv/pr106602.c
 create mode 100644 gcc/testsuite/gcc.target/riscv/pr95632.c

diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index df57e2b0b4a..0a9b5ec22b0 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -1667,6 +1667,22 @@
 		      MAX_MACHINE_MODE, &operands[3], TRUE);
 })
 
+;; Pretend to have the ability to load complex const_int in order to get
+;; better code generation around them.
+(define_insn_and_split ""
+  [(set (match_operand:GPR 0 "register_operand" "=r")
+    (match_operand:GPR 1 "splittable_const_int_operand" "i"))]
+  "cse_not_expected"
+  "#"
+  "&& 1"
+  [(const_int 0)]
+
+{
+  riscv_move_integer (operands[0], operands[0], INTVAL (operands[1]),
+		      <GPR:MODE>mode, TRUE);
+  DONE;
+})
+
 ;; 64-bit integer moves
 
 (define_expand "movdi"
diff --git a/gcc/testsuite/gcc.target/riscv/pr106602.c b/gcc/testsuite/gcc.target/riscv/pr106602.c
new file mode 100644
index 00000000000..83b70877012
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr106602.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=rv64gc" } */
+
+unsigned long
+foo2 (unsigned long a)
+{
+  return (unsigned long)(unsigned int) a << 6;
+}
+
+/* { dg-final { scan-assembler-times "slli\t" 1 } } */
+/* { dg-final { scan-assembler-times "srli\t" 1 } } */
+/* { dg-final { scan-assembler-not "\tli\t" } } */
+/* { dg-final { scan-assembler-not "addi\t" } } */
+/* { dg-final { scan-assembler-not "and\t" } } */
diff --git a/gcc/testsuite/gcc.target/riscv/pr95632.c b/gcc/testsuite/gcc.target/riscv/pr95632.c
new file mode 100644
index 00000000000..bd316ab1d7b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr95632.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=rv32imafc -mabi=ilp32f" } */
+
+unsigned short
+foo (unsigned short crc)
+{
+  crc ^= 0x4002;
+  crc >>= 1;
+  crc |= 0x8000;
+
+  return crc;
+}
+
+/* { dg-final { scan-assembler-times "srli\t" 1 } } */
+/* { dg-final { scan-assembler-not "slli\t" } } */
-- 
2.38.1