synth: fix handling of multi-dim ROM. Fix #1390

Document index order for memidx.

3 files changed, 26 insertions, 24 deletions

diff --git a/src/synth/netlists-gates.ads b/src/synth/netlists-gates.ads
index 990331bf9..4acf9f6b4 100644
--- a/src/synth/netlists-gates.ads
+++ b/src/synth/netlists-gates.ads
@@ -257,12 +257,21 @@ package Netlists.Gates is
    subtype Dyn_Insert_Module_Id is
      Module_Id range Id_Dyn_Insert .. Id_Dyn_Insert_En;
 
+   --  Gate to compute dynamic insert or extract offsets.
+   --  Provides the scale (step) factor (needed for insert/extract wider than
+   --   1 bit), also provides the maximum index value.
+   --  For multi-dimensional insert/extract, memidx needs to be combined with
+   --   addidx.
    --  Inputs:  0: index
    --  Params:  0: step
    --           1: max
    --  OUT := IN0 * STEP,  IN0 < MAX
    Id_Memidx : constant Module_Id := 90;
 
+   --  Combine (simply add) indexes for dynamic insert or extract.
+   --  Despite the addition being commutative, the inputs are ordered.
+   --  Input 0 must be a memidx (the most significant one, so with the larger
+   --   step), and input 1 must be either a memidx or an addidx.
    --  OUT := IN0 + IN1, size extension (max of inputs width).
    --  Inputs:  0: a memidx
    --           1: chain (addidx or memidx).
diff --git a/src/synth/netlists-memories.adb b/src/synth/netlists-memories.adb
index 704c96e8b..f9e5c124c 100644
--- a/src/synth/netlists-memories.adb
+++ b/src/synth/netlists-memories.adb
@@ -165,10 +165,10 @@ package body Netlists.Memories is
                when Id_Dyn_Extract =>
                   --  Extract step from memidx gate.
                   Idx := Get_Net_Parent (Get_Input_Net (Extr_Inst, 1));
-                  if Get_Id (Idx) = Id_Addidx then
-                     --  Multi-dim arrays, lowest index is the first one.
-                     Idx := Get_Net_Parent (Get_Input_Net (Idx, 0));
-                  end if;
+                  while Get_Id (Idx) = Id_Addidx loop
+                     --  Multi-dim arrays, lowest index is the last one.
+                     Idx := Get_Net_Parent (Get_Input_Net (Idx, 1));
+                  end loop;
                   pragma Assert (Get_Id (Idx) = Id_Memidx);
                   Step := Get_Param_Uns32 (Idx, 0);
 
@@ -316,7 +316,7 @@ package body Netlists.Memories is
       pragma Unreferenced (Mem_Depth);
 
       --  Do checks on memidx.
-      Last_Size := 0;
+      Last_Size := Mem_Size;
       for I in Indexes'Range loop
          declare
             Inst : constant Instance := Indexes (I).Inst;
@@ -326,17 +326,18 @@ package body Netlists.Memories is
             Max : constant Uns32 := Get_Param_Uns32 (Inst, 1);
             Max_W : constant Width := Clog2 (Max + 1);
             Sub_Addr1 : Net;
+            Sz : Uns32;
          begin
             --  Check max (from previous dimension).
+            --  Check the memidx can index its whole input.
             pragma Assert (Max /= 0);
-            if I /= Indexes'First then
-               if Last_Size /= Step then
-                  raise Internal_Error;
-               end if;
+            Sz := (Max + 1) * Step;
+            if Sz /= Last_Size then
+               raise Internal_Error;
             end if;
-            Last_Size := (Max + 1) * Step;
+            Last_Size := Step;
 
-            if I = Indexes'First then
+            if I = Indexes'Last then
                if Step /= Val_Wd then
                   raise Internal_Error;
                end if;
@@ -357,16 +358,12 @@ package body Netlists.Memories is
          end;
       end loop;
 
-      if Last_Size /= Mem_Size then
-         raise Internal_Error;
-      end if;
-
       --  Lower (just concat addresses).
       declare
          use Netlists.Concats;
          Concat : Concat_Type;
       begin
-         for I in Indexes'Range loop
+         for I in reverse Indexes'Range loop
             Append (Concat, Indexes (I).Addr);
          end loop;
 
diff --git a/src/synth/synth-expr.adb b/src/synth/synth-expr.adb
index 85404d7e3..654d25eb8 100644
--- a/src/synth/synth-expr.adb
+++ b/src/synth/synth-expr.adb
@@ -1167,16 +1167,10 @@ package body Synth.Expr is
       Voff := No_Net;
       Off := (0, 0);
 
-      for I in Flist_First .. Flist_Last (Indexes) loop
+      Stride := 1;
+      for I in reverse Flist_First .. Flist_Last (Indexes) loop
          Idx_Expr := Get_Nth_Element (Indexes, I);
 
-         --  Compute stride.  This is O(n**2), but for small n.
-         Stride := 1;
-         for J in I + 1 .. Flist_Last (Indexes) loop
-            Bnd := Get_Array_Bound (Pfx_Type, Dim_Type (J + 1));
-            Stride := Stride * Bnd.Len;
-         end loop;
-
          --  Use the base type as the subtype of the index is not synth-ed.
          Idx_Val := Synth_Expression_With_Basetype (Syn_Inst, Idx_Expr);
          Strip_Const (Idx_Val);
@@ -1204,6 +1198,8 @@ package body Synth.Expr is
                Set_Location (Voff, Idx_Expr);
             end if;
          end if;
+
+         Stride := Stride * Bnd.Len;
       end loop;
    end Synth_Indexed_Name;