[gcc r13-3845] RISC-V: costs: handle BSWAP

[Philipp Tomsich <ptomsich@gcc.gnu.org>]

https://gcc.gnu.org/g:e7c8f5005bf87e4bd95b25fb31430eef7e58097e

commit r13-3845-ge7c8f5005bf87e4bd95b25fb31430eef7e58097e
Author: Philipp Tomsich <philipp.tomsich@vrull.eu>
Date:   Fri Dec 18 10:00:34 2020 +0100

    RISC-V: costs: handle BSWAP
    
    The BSWAP operation is not handled in rtx_costs. Add it.
    
    With Zbb, BSWAP for XLEN is a single instruction; for smaller modes,
    it will expand into two.
    
    gcc/ChangeLog:
    
            * config/riscv/riscv.cc (riscv_rtx_costs): Add BSWAP.

Diff:
---
 gcc/config/riscv/riscv.cc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 32f9ef9ade9..ab6c745c722 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -2562,6 +2562,16 @@ riscv_rtx_costs (rtx x, machine_mode mode, int outer_code, int opno ATTRIBUTE_UN
       *total = riscv_extend_cost (XEXP (x, 0), GET_CODE (x) == ZERO_EXTEND);
       return false;
 
+    case BSWAP:
+      if (TARGET_ZBB)
+	{
+	  /* RISC-V only defines rev8 for XLEN, so we will need an extra
+	     shift-right instruction for smaller modes. */
+	  *total = COSTS_N_INSNS (mode == word_mode ? 1 : 2);
+	  return true;
+	}
+      return false;
+
     case FLOAT:
     case UNSIGNED_FLOAT:
     case FIX: