From 6d69d4aaa81f176ec97654b5103f6f59eb98c211 Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Thu, 17 Jul 2014 13:13:21 +0200
Subject: [PATCH] Added support for constant bit- or part-select for memory
 writes

---
 frontends/ast/simplify.cc | 45 +++++++++++++++++++++++++++++++--------
 tests/simple/memory.v     | 20 +++++++++++++++++
 2 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index ba0dca139..320c80d72 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -607,9 +607,9 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 	}
 
 	// split memory access with bit select to individual statements
-	if (type == AST_IDENTIFIER && children.size() == 2 && children[0]->type == AST_RANGE && children[1]->type == AST_RANGE)
+	if (type == AST_IDENTIFIER && children.size() == 2 && children[0]->type == AST_RANGE && children[1]->type == AST_RANGE && !in_lvalue)
 	{
-		if (id2ast == NULL || id2ast->type != AST_MEMORY || children[0]->children.size() != 1 || in_lvalue)
+		if (id2ast == NULL || id2ast->type != AST_MEMORY || children[0]->children.size() != 1)
 			log_error("Invalid bit-select on memory access at %s:%d!\n", filename.c_str(), linenum);
 
 		int mem_width, mem_size, addr_bits;
@@ -1150,9 +1150,9 @@ skip_dynamic_range_lvalue_expansion:;
 
 	// assignment with memory in left-hand side expression -> replace with memory write port
 	if (stage > 1 && (type == AST_ASSIGN_EQ || type == AST_ASSIGN_LE) && children[0]->type == AST_IDENTIFIER &&
-			children[0]->children.size() == 1 && children[0]->id2ast && children[0]->id2ast->type == AST_MEMORY &&
-			children[0]->id2ast->children.size() >= 2 && children[0]->id2ast->children[0]->range_valid &&
-			children[0]->id2ast->children[1]->range_valid)
+			children[0]->id2ast && children[0]->id2ast->type == AST_MEMORY && children[0]->id2ast->children.size() >= 2 &&
+			children[0]->id2ast->children[0]->range_valid && children[0]->id2ast->children[1]->range_valid &&
+			(children[0]->children.size() == 1 || children[0]->children.size() == 2))
 	{
 		std::stringstream sstr;
 		sstr << "$memwr$" << children[0]->str << "$" << filename << ":" << linenum << "$" << (RTLIL::autoidx++);
@@ -1209,11 +1209,38 @@ skip_dynamic_range_lvalue_expansion:;
 		assign_addr = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), children[0]->children[0]->children[0]->clone());
 		assign_addr->children[0]->str = id_addr;
 
-		assign_data = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), children[1]->clone());
-		assign_data->children[0]->str = id_data;
+		if (children[0]->children.size() == 2)
+		{
+			if (children[0]->children[1]->range_valid)
+			{
+				int offset = children[0]->children[1]->range_right;
+				int width = children[0]->children[1]->range_left - offset + 1;
 
-		assign_en = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), mkconst_bits(set_bits_en, false));
-		assign_en->children[0]->str = id_en;
+				std::vector<RTLIL::State> padding_x(offset, RTLIL::State::Sx);
+
+				for (int i = 0; i < mem_width; i++)
+					set_bits_en[i] = offset <= i && i < offset+width ? RTLIL::State::S1 : RTLIL::State::S0;
+
+				assign_data = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER),
+						new AstNode(AST_CONCAT, mkconst_bits(padding_x, false), children[1]->clone()));
+				assign_data->children[0]->str = id_data;
+
+				assign_en = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), mkconst_bits(set_bits_en, false));
+				assign_en->children[0]->str = id_en;
+			}
+			else
+			{
+				log_error("Writing to memories with dynamic bit- or part-select is not supported yet at %s:%d.\n", filename.c_str(), linenum);
+			}
+		}
+		else
+		{
+			assign_data = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), children[1]->clone());
+			assign_data->children[0]->str = id_data;
+
+			assign_en = new AstNode(AST_ASSIGN_LE, new AstNode(AST_IDENTIFIER), mkconst_bits(set_bits_en, false));
+			assign_en->children[0]->str = id_en;
+		}
 
 		newNode = new AstNode(AST_BLOCK);
 		newNode->children.push_back(assign_addr);
diff --git a/tests/simple/memory.v b/tests/simple/memory.v
index 927ee0438..aae3feace 100644
--- a/tests/simple/memory.v
+++ b/tests/simple/memory.v
@@ -114,3 +114,23 @@ assign rd_data = memory[rd_addr_buf];
 
 endmodule
 
+// ----------------------------------------------------------
+
+module test05(clk, addr, wdata, rdata, wen);
+
+input clk;
+input [1:0] addr;
+input [7:0] wdata;
+output reg [7:0] rdata;
+input [3:0] wen;
+
+reg [7:0] mem [0:3];
+
+integer i;
+always @(posedge clk) begin
+	for (i = 0; i < 4; i = i+1)
+		if (wen[i]) mem[addr][i*2 +: 2] <= wdata[i*2 +: 2];
+	rdata <= mem[addr];
+end
+
+endmodule
-- 
2.30.2