RISC-V: No extensions for SImode min/max against safe constant

Optimize the common case of a SImode min/max against a constant
that is safe both for sign- and zero-extension.
E.g., consider the case
  int f(unsigned int* a)
  {
    const int C = 1000;
    return *a * 3 > C ? C : *a * 3;
  }
where the constant C will yield the same result in DImode whether
sign- or zero-extended.

This should eventually go away once the lowering to RTL smartens up
and considers the precision/signedness and the value-ranges of the
operands to MIN_EXPR and MAX_EXPR.

gcc/ChangeLog:

	* config/riscv/bitmanip.md (*minmax): Additional pattern for
	  min/max against constants that are extension-invariant.
	* config/riscv/iterators.md (minmax_optab): Add an iterator
	  that has only min and max rtl.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zbb-min-max-02.c: New test.

3 files changed, 36 insertions, 0 deletions

diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 58bac72..d17133d 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -368,6 +368,24 @@
   "<bitmanip_insn>\t%0,%1,%2"
   [(set_attr "type" "bitmanip")])
 
+;; Optimize the common case of a SImode min/max against a constant
+;; that is safe both for sign- and zero-extension.
+(define_insn_and_split "*minmax"
+  [(set (match_operand:DI 0 "register_operand" "=r")
+	(sign_extend:DI
+	  (subreg:SI
+	    (bitmanip_minmax:DI (zero_extend:DI (match_operand:SI 1 "register_operand" "r"))
+						(match_operand:DI 2 "immediate_operand" "i"))
+	   0)))
+   (clobber (match_scratch:DI 3 "=&r"))
+   (clobber (match_scratch:DI 4 "=&r"))]
+  "TARGET_64BIT && TARGET_ZBB && sext_hwi (INTVAL (operands[2]), 32) >= 0"
+  "#"
+  "&& reload_completed"
+  [(set (match_dup 3) (sign_extend:DI (match_dup 1)))
+   (set (match_dup 4) (match_dup 2))
+   (set (match_dup 0) (<minmax_optab>:DI (match_dup 3) (match_dup 4)))])
+
 ;; ZBS extension.
 
 (define_insn "*bset<mode>"
diff --git a/gcc/config/riscv/iterators.md b/gcc/config/riscv/iterators.md
index ab1f4ee..efdd3cc 100644
--- a/gcc/config/riscv/iterators.md
+++ b/gcc/config/riscv/iterators.md
@@ -221,6 +221,10 @@
   [(plus "add") (ior "or") (xor "xor") (and "and")])
 
 ; bitmanip code attributes
+(define_code_attr minmax_optab [(smin "smin")
+				(smax "smax")
+				(umin "umin")
+				(umax "umax")])
 (define_code_attr bitmanip_optab [(smin "smin")
 				  (smax "smax")
 				  (umin "umin")
diff --git a/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c b/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c
new file mode 100644
index 0000000..b462859
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zba_zbb -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-O1" "-Os" "-Oz" "-Og" } } */
+
+int f(unsigned int* a)
+{
+  const int C = 1000;
+  return *a * 3 > C ? C : *a * 3;
+}
+
+/* { dg-final { scan-assembler-times "minu" 1 } } */
+/* { dg-final { scan-assembler-times "sext.w" 1 } } */
+/* { dg-final { scan-assembler-not "zext.w" } } */
+