[PATCH] RISC-V: branch-(not)equals-zero compares against $zero

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

If we are testing a register or a paradoxical subreg (i.e. anything that is not
a partial subreg) for equality/non-equality with zero, we can generate a branch
that compares against $zero.  This will work for QI, HI, SI and DImode, so we
enable this for ANYI.

2020-08-30  gcc/ChangeLog:

	* config/riscv/riscv.md (*branch<mode>_equals_zero): Added pattern.

---

 gcc/config/riscv/riscv.md | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 798f7370a08..97f6ca37891 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -2205,6 +2205,19 @@
 
 ;; Conditional branches
 
+(define_insn "*branch<mode>_equals_zero"
+  [(set (pc)
+	(if_then_else
+	 (match_operator 1 "equality_operator"
+			 [(match_operand:ANYI 2 "register_operand" "r")
+			  (const_int 0)])
+	 (label_ref (match_operand 0 "" ""))
+	 (pc)))]
+  "!partial_subreg_p (operands[2])"
+  "b%C1\t%2,zero,%0"
+  [(set_attr "type" "branch")
+   (set_attr "mode" "none")])
+
 (define_insn "*branch<mode>"
   [(set (pc)
 	(if_then_else
-- 
2.34.1