loadstore1: Better expression for store data formatting

This rearranges the code used for store data formatting so that the
"for i in 0 to 7" loop indexes the output bytes rather than the
input bytes.  The new expression is formally identical to the old
but is easier to synthesize.  This reduces the number of LUTs by
about 250 on the Artix-7 and improves timing.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

diff --git a/loadstore1.vhdl b/loadstore1.vhdl
index 87f471082e460e79d20c3fc6bfb3b7ebf9be6f6d..62914c06fbc877dfd339d378f1aae484644a1ec0 100644 (file)
--- a/loadstore1.vhdl
+++ b/loadstore1.vhdl
@@ -159,6 +159,7 @@ begin
         variable done : std_ulogic;
         variable data_permuted : std_ulogic_vector(63 downto 0);
         variable data_trimmed : std_ulogic_vector(63 downto 0);
+        variable store_data : std_ulogic_vector(63 downto 0);
         variable use_second : byte_sel_t;
         variable trim_ctl : trim_ctl_t;
         variable negative : std_ulogic;
@@ -232,6 +233,23 @@ begin
             end case;
         end loop;
 
+        -- Byte reversing and rotating for stores
+        -- Done in the first cycle (when l_in.valid = 1)
+        store_data := r.store_data;
+        if l_in.valid = '1' then
+            byte_offset := unsigned(lsu_sum(2 downto 0));
+            brev_lenm1 := "000";
+            if l_in.byte_reverse = '1' then
+                brev_lenm1 := unsigned(l_in.length(2 downto 0)) - 1;
+            end if;
+            for i in 0 to 7 loop
+                k := (to_unsigned(i, 3) - byte_offset) xor brev_lenm1;
+                j := to_integer(k) * 8;
+                store_data(i * 8 + 7 downto i * 8) := l_in.data(j + 7 downto j);
+            end loop;
+        end if;
+        v.store_data := store_data;
+
         -- compute (addr + 8) & ~7 for the second doubleword when unaligned
         next_addr := std_ulogic_vector(unsigned(r.addr(63 downto 3)) + 1) & "000";
 
@@ -379,18 +397,6 @@ begin
             v.first_bytes := byte_sel;
             v.second_bytes := long_sel(15 downto 8);
 
-            -- Do byte reversing and rotating for stores in the first cycle
-            byte_offset := unsigned(lsu_sum(2 downto 0));
-            brev_lenm1 := "000";
-            if l_in.byte_reverse = '1' then
-                brev_lenm1 := unsigned(l_in.length(2 downto 0)) - 1;
-            end if;
-            for i in 0 to 7 loop
-                k := (to_unsigned(i, 3) xor brev_lenm1) + byte_offset;
-                j := to_integer(k) * 8;
-                v.store_data(j + 7 downto j) := l_in.data(i * 8 + 7 downto i * 8);
-            end loop;
-
             case l_in.op is
                 when OP_STORE =>
                     req := '1';
@@ -465,7 +471,7 @@ begin
         d_out.nc <= v.nc;
         d_out.reserve <= v.reserve;
         d_out.addr <= addr;
-        d_out.data <= v.store_data;
+        d_out.data <= store_data;
         d_out.byte_sel <= byte_sel;
         d_out.virt_mode <= v.virt_mode;
         d_out.priv_mode <= v.priv_mode;