Zicond: implement Zicond (conditional integer operations)

This implements the Zicond (conditional integer operations) extension,
as of version 1.0-draft-20230120.

The Zicond extension acts as a building block for branchless sequences
including conditional-arithmetic, conditional-logic and
conditional-select/move.
The following instructions constitute Zicond:
 - czero.eqz rd, rs1, rs2  =>  rd = (rs2 == 0) ? 0 : rs1
 - czero.nez rd, rs1, rs2  =>  rd = (rs2 != 0) ? 0 : rs1

See
  https://github.com/riscv/riscv-zicond/releases/download/v1.0-draft-20230120/riscv-zicond_1.0-draft-20230120.pdf
for the proposed specification and usage details.

2 files changed, 4 insertions, 0 deletions

diff --git a/riscv/insns/czero_eqz.h b/riscv/insns/czero_eqz.h
new file mode 100644
index 0000000..24062af
--- /dev/null
+++ b/riscv/insns/czero_eqz.h
@@ -0,0 +1,2 @@
+require_extension(EXT_ZICOND);
+WRITE_RD(RS2 == 0 ? 0 : RS1);
diff --git a/riscv/insns/czero_nez.h b/riscv/insns/czero_nez.h
new file mode 100644
index 0000000..cd6c8af
--- /dev/null
+++ b/riscv/insns/czero_nez.h
@@ -0,0 +1,2 @@
+require_extension(EXT_ZICOND);
+WRITE_RD(RS2 != 0 ? 0 : RS1);