cxxrtl: fix rzext().

This was a correctness issue, but one of the consequences is that it
resulted in jumps in generated machine code where there should have
been none. As a side effect of fixing the bug, Minerva SoC became 10%
faster.

diff --git a/backends/cxxrtl/cxxrtl.h b/backends/cxxrtl/cxxrtl.h
index ce21cc1e6502ab1d797b432d4f3c5a6d533fadd6..10184bb3f7ca999983157892b0d6d5b52e823e68 100644 (file)
--- a/backends/cxxrtl/cxxrtl.h
+++ b/backends/cxxrtl/cxxrtl.h
@@ -165,8 +165,8 @@ struct value : public expr_base<value<Bits>> {
                        carry = (shift_bits == 0) ? 0
                                : data[n] >> (chunk::bits - shift_bits);
                }
-               if (carry != 0)
-                       result.data[result.chunks - 1] = carry;
+               if (shift_chunks + chunks < result.chunks)
+                       result.data[shift_chunks + chunks] = carry;
                return result;
        }