From 1f2c340b7a8df661f31a1f0fdbac2bf69da7f463 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Sun, 1 Aug 2021 23:02:59 +0800
Subject: [PATCH] Try to reduce unnecessary lowering of left/right

---
 src/lower.c | 44 ++++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 12 deletions(-)

diff --git a/src/lower.c b/src/lower.c
index cfc62d81..1749b583 100644
--- a/src/lower.c
+++ b/src/lower.c
@@ -318,9 +318,30 @@ static vcode_reg_t lower_array_data(vcode_reg_t reg)
    }
 }
 
+static bool lower_should_use_uarray(type_t type, int dim, vcode_reg_t reg)
+{
+   if (reg == VCODE_INVALID_REG)
+      return false;
+   else if (type_is_unconstrained(type))
+      return true;
+   else if (vcode_reg_kind(reg) != VCODE_TYPE_UARRAY)
+      return false;
+   else {
+      tree_t r = range_of(type, dim);
+      if (tree_subkind(r) == RANGE_EXPR)
+         return false;
+
+      const tree_kind_t lkind = tree_kind(tree_left(r));
+      const tree_kind_t rkind = tree_kind(tree_right(r));
+
+      return (lkind != T_LITERAL && lkind != T_REF)
+         || (rkind != T_LITERAL && rkind != T_REF);
+   }
+}
+
 static vcode_reg_t lower_array_left(type_t type, int dim, vcode_reg_t reg)
 {
-   if (type_is_unconstrained(type)) {
+   if (lower_should_use_uarray(type, dim, reg)) {
       assert(reg != VCODE_INVALID_REG);
       type_t index_type = index_type_of(type, dim);
       return emit_cast(lower_type(index_type), lower_bounds(index_type),
@@ -332,7 +353,7 @@ static vcode_reg_t lower_array_left(type_t type, int dim, vcode_reg_t reg)
 
 static vcode_reg_t lower_array_right(type_t type, int dim, vcode_reg_t reg)
 {
-   if (type_is_unconstrained(type)) {
+   if (lower_should_use_uarray(type, dim, reg)) {
       assert(reg != VCODE_INVALID_REG);
       type_t index_type = index_type_of(type, dim);
       return emit_cast(lower_type(index_type), lower_bounds(index_type),
@@ -344,7 +365,7 @@ static vcode_reg_t lower_array_right(type_t type, int dim, vcode_reg_t reg)
 
 static vcode_reg_t lower_array_dir(type_t type, int dim, vcode_reg_t reg)
 {
-   if (type_is_unconstrained(type)) {
+   if (lower_should_use_uarray(type, dim, reg)) {
       assert(reg != VCODE_INVALID_REG);
       assert(vcode_reg_kind(reg) == VCODE_TYPE_UARRAY);
       return emit_uarray_dir(reg, dim);
@@ -357,7 +378,7 @@ static vcode_reg_t lower_array_dir(type_t type, int dim, vcode_reg_t reg)
 
 static vcode_reg_t lower_array_len(type_t type, int dim, vcode_reg_t reg)
 {
-   if (type_is_unconstrained(type)) {
+   if (lower_should_use_uarray(type, dim, reg)) {
       assert(reg != VCODE_INVALID_REG);
       return emit_uarray_len(reg, dim);
    }
@@ -4984,21 +5005,20 @@ static void lower_signal_decl(tree_t decl)
                               name, VAR_SIGNAL);
    lower_put_vcode_obj(decl, var, top_scope);
 
-   vcode_reg_t shared = VCODE_INVALID_REG;
+   vcode_reg_t shared, wrapped;
    if (vtype_kind(signal_type) == VCODE_TYPE_UARRAY) {
       shared = emit_link_signal(name, vtype_elem(signal_type));
-      emit_store(lower_wrap(type, shared), var);
-   }
-   else {
-      shared = emit_link_signal(name, signal_type);
-      emit_store(shared, var);
+      wrapped = lower_wrap(type, shared);
    }
+   else
+      shared = wrapped = emit_link_signal(name, signal_type);
+
+   emit_store(wrapped, var);
 
    tree_t value = tree_value(decl);
    vcode_reg_t init_reg = lower_expr(value, EXPR_RVALUE), len_reg;
    if (type_is_array(tree_type(value))) {
-      lower_check_array_sizes(decl, type, tree_type(value),
-                              VCODE_INVALID_REG, init_reg);
+      lower_check_array_sizes(decl, type, tree_type(value), shared, init_reg);
       init_reg = lower_array_data(init_reg);
       len_reg  = lower_array_total_len(type, init_reg);
    }
-- 
2.39.2