Some bugfixes for CSR reading and setting FS for fflags updates (#43)

* csrrc[i] and csrrs[i] don't write CSRs if rs/zimm == 0

* Dirty fp state when setting new fp exceptions

* Set FS to dirty for all non-zero fflags writes.

4 files changed, 20 insertions, 8 deletions

diff --git a/riscv/insns/csrrc.h b/riscv/insns/csrrc.h
index 74a6872..eae91fe 100644
--- a/riscv/insns/csrrc.h
+++ b/riscv/insns/csrrc.h
@@ -1,4 +1,7 @@
-int csr = validate_csr(insn.csr(), true);
+bool write = insn.rs1() != 0;
+int csr = validate_csr(insn.csr(), write);
 reg_t old = p->get_csr(csr);
-p->set_csr(csr, old & ~RS1);
+if (write) {
+  p->set_csr(csr, old & ~RS1);
+}
 WRITE_RD(sext_xlen(old));
diff --git a/riscv/insns/csrrci.h b/riscv/insns/csrrci.h
index 993f2d8..986d601 100644
--- a/riscv/insns/csrrci.h
+++ b/riscv/insns/csrrci.h
@@ -1,4 +1,7 @@
-int csr = validate_csr(insn.csr(), true);
+bool write = insn.rs1() != 0;
+int csr = validate_csr(insn.csr(), write);
 reg_t old = p->get_csr(csr);
-p->set_csr(csr, old & ~(reg_t)insn.rs1());
+if (write) {
+  p->set_csr(csr, old & ~(reg_t)insn.rs1());
+}
 WRITE_RD(sext_xlen(old));
diff --git a/riscv/insns/csrrs.h b/riscv/insns/csrrs.h
index 72b49bb..ec61b42 100644
--- a/riscv/insns/csrrs.h
+++ b/riscv/insns/csrrs.h
@@ -1,4 +1,7 @@
-int csr = validate_csr(insn.csr(), insn.rs1() != 0);
+bool write = insn.rs1() != 0;
+int csr = validate_csr(insn.csr(), write);
 reg_t old = p->get_csr(csr);
-p->set_csr(csr, old | RS1);
+if (write) {
+  p->set_csr(csr, old | RS1);
+}
 WRITE_RD(sext_xlen(old));
diff --git a/riscv/insns/csrrsi.h b/riscv/insns/csrrsi.h
index 90a4436..aa44dcc 100644
--- a/riscv/insns/csrrsi.h
+++ b/riscv/insns/csrrsi.h
@@ -1,4 +1,7 @@
-int csr = validate_csr(insn.csr(), true);
+bool write = insn.rs1() != 0;
+int csr = validate_csr(insn.csr(), write);
 reg_t old = p->get_csr(csr);
-p->set_csr(csr, old | insn.rs1());
+if (write) {
+  p->set_csr(csr, old | insn.rs1());
+}
 WRITE_RD(sext_xlen(old));