On 11/13/22 16:05, Christoph Muellner wrote:
From: Christoph Müllner <christoph.muell...@vrull.eu>
This patch implements the expansion of the strlen builtin
using Zbb instructions (if available) for aligned strings
using the following sequence:
li a3,-1
addi a4,a0,8
.L2: ld a5,0(a0)
addi a0,a0,8
orc.b a5,a5
beq a5,a3,6 <.L2>
not a5,a5
ctz a5,a5
srli a5,a5,0x3
add a0,a0,a5
sub a0,a0,a4
This allows to inline calls to strlen(), with optimized code for
determining the length of a string.
gcc/ChangeLog:
* config/riscv/riscv-protos.h (riscv_expand_strlen): New
prototype.
* config/riscv/riscv-string.cc (riscv_emit_unlikely_jump): New
function.
(GEN_EMIT_HELPER2): New helper macro.
(GEN_EMIT_HELPER3): New helper macro.
(do_load_from_addr): New helper function.
(riscv_expand_strlen_zbb): New function.
(riscv_expand_strlen): New function.
* config/riscv/riscv.md (strlen<mode>): Invoke expansion
functions for strlen.
+extern bool riscv_expand_strlen (rtx[]);
Consider adding the number of elements in the RTX array here. Martin S's
work from a little while ago will make use of it to try and catch
over-reads and over-writes if the data is available.
/* Information about one CPU we know about. */
struct riscv_cpu_info {
diff --git a/gcc/config/riscv/riscv-string.cc b/gcc/config/riscv/riscv-string.cc
index 1137df475be..bf96522b608 100644
--- a/gcc/config/riscv/riscv-string.cc
+++ b/gcc/config/riscv/riscv-string.cc
@@ -38,6 +38,81 @@
#include "predict.h"
#include "optabs.h"
+/* Emit unlikely jump instruction. */
+
+static rtx_insn *
+riscv_emit_unlikely_jump (rtx insn)
+{
+ rtx_insn *jump = emit_jump_insn (insn);
+ add_reg_br_prob_note (jump, profile_probability::very_unlikely ());
+ return jump;
+}
I was a bit surprised that we didn't have this as a generic routine.
Consider adding this to emit-rtl.cc along with its companion
emit_likely_jump. Not a requirement to move forward, but it seems like
the right thing to do.
+
+/* Emit proper instruction depending on type of dest. */
s/type/mode/
+
+/* Emit proper instruction depending on type of dest. */
s/type/mode/
You probably want to undefine GEN_EMIT_HELPER once you're done when
them. That's become fairly standard practice for these kind of helper
macros.
OK with the nits fixed. Your call on whether or not to move the
implementation of emit_likely_jump and emit_unlikely_jump into emit-rtl.cc.
Jeff
