From a2e69560aba874f2b93094841e79230412f93c3f Mon Sep 17 00:00:00 2001
From: Dag Lem <dag@nimrod.no>
Date: Tue, 8 Aug 2023 12:11:54 +0200
Subject: [PATCH] Optimization of nowrshmsk

The stride implification of the generated AST_CASE is generalized to
handle variable slices on the form dst[i*stride +: width] = src

To avoid optimization issues, the simplification of the non_opt_range
AST is reverted, and the removal of multiplication of index by stride
is temporarily disabled.
---
 frontends/ast/simplify.cc             | 27 +++++++++++++++++++--------
 frontends/verilog/verilog_parser.y    | 12 ++++++------
 tests/svtypes/struct_dynamic_range.ys |  2 +-
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 53ffcc2810c..cdfaaa6c9aa 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2863,18 +2863,29 @@ bool AstNode::simplify(bool const_fold, bool in_lvalue, int stage, int width_hin
 			int stride = 1;
 			int div_stride = 1;
 
-			// Optimization: Remove multiplication of index by stride for two-dimensional packed arrays and
-			// variable slices on the form dst[i*w +: w] = src.
-			if (!source_offset && shift_expr->type == AST_MUL &&
-			    ((shift_expr->children[0]->type == AST_CONSTANT && (int)shift_expr->children[0]->integer == result_width) ||
-			     (shift_expr->children[1]->type == AST_CONSTANT && (int)shift_expr->children[1]->integer == result_width)))
+			// Extract (index)*(width) from non_opt_range pattern (@selfsz@((index)*(width)))+(0)).
+			AstNode *lsb_expr =
+				shift_expr->type == AST_ADD && shift_expr->children[0]->type == AST_SELFSZ &&
+				shift_expr->children[1]->type == AST_CONSTANT && shift_expr->children[1]->integer == 0 ?
+				shift_expr->children[0]->children[0] :
+				shift_expr;
+
+			// Optimization: Extract stride from indexing of two-dimensional packed arrays and
+			// variable slices on the form dst[i*stride +: width] = src.
+			if (!source_offset && lsb_expr->type == AST_MUL &&
+			    (lsb_expr->children[0]->type == AST_CONSTANT || lsb_expr->children[1]->type == AST_CONSTANT))
 			{
-				int var_i = shift_expr->children[0]->type == AST_CONSTANT;
-				AstNode *tmp = shift_expr->children[var_i]->clone();
-				stride = result_width;
+				int const_i = lsb_expr->children[1]->type == AST_CONSTANT;
+				stride = (int)lsb_expr->children[const_i]->integer;
+
+				// Remove multiplication of index by stride.
+				// FIXME: Counterintuitively, this can yield higher resource usage. Disable for now.
+#if 0
 				div_stride = stride;
+				AstNode *tmp = lsb_expr->children[1 - const_i]->clone();
 				delete shift_expr;
 				shift_expr = tmp;
+#endif
 			}
 			else if (member_node)  // Member in packed struct/union
 			{
diff --git a/frontends/verilog/verilog_parser.y b/frontends/verilog/verilog_parser.y
index ee89aecace9..98bdbf9e5c5 100644
--- a/frontends/verilog/verilog_parser.y
+++ b/frontends/verilog/verilog_parser.y
@@ -884,15 +884,15 @@ non_opt_range:
 	} |
 	'[' expr TOK_POS_INDEXED expr ']' {
 		$$ = new AstNode(AST_RANGE);
-		AstNode *expr = new AstNode(AST_SELFSZ, $2->clone());
-		$$->children.push_back(new AstNode(AST_SUB, new AstNode(AST_ADD, expr, $4), AstNode::mkconst_int(1, true)));
-		$$->children.push_back($2);
+		AstNode *expr = new AstNode(AST_SELFSZ, $2);
+		$$->children.push_back(new AstNode(AST_SUB, new AstNode(AST_ADD, expr->clone(), $4), AstNode::mkconst_int(1, true)));
+		$$->children.push_back(new AstNode(AST_ADD, expr, AstNode::mkconst_int(0, true)));
 	} |
 	'[' expr TOK_NEG_INDEXED expr ']' {
 		$$ = new AstNode(AST_RANGE);
-		AstNode *expr = new AstNode(AST_SELFSZ, $2->clone());
-		$$->children.push_back($2);
-		$$->children.push_back(new AstNode(AST_SUB, new AstNode(AST_ADD, expr, AstNode::mkconst_int(1, true)), $4));
+		AstNode *expr = new AstNode(AST_SELFSZ, $2);
+		$$->children.push_back(new AstNode(AST_ADD, expr, AstNode::mkconst_int(0, true)));
+		$$->children.push_back(new AstNode(AST_SUB, new AstNode(AST_ADD, expr->clone(), AstNode::mkconst_int(1, true)), $4));
 	} |
 	'[' expr ']' {
 		$$ = new AstNode(AST_RANGE);
diff --git a/tests/svtypes/struct_dynamic_range.ys b/tests/svtypes/struct_dynamic_range.ys
index 3891c2b3a8b..9606e73840c 100644
--- a/tests/svtypes/struct_dynamic_range.ys
+++ b/tests/svtypes/struct_dynamic_range.ys
@@ -1,5 +1,5 @@
 read_verilog -sv struct_dynamic_range.sv
-select -assert-count 3 t:$mul
+select -assert-count 4 t:$mul
 select -assert-count 2 t:$shift
 select -assert-count 2 t:$shiftx
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