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Avoid generating useless `wait for 0ns' statements 

If the final statement in a process is a non-blocking
assignment then there is no point adding a `wait for 0ns'
after it since it will be immediately followed by another
wait. This case is suprisingly common, so this patch helps
generate much cleaner output without breaking the cases
where the 0ns wait is actually required (e.g. to implement
non-blocking assignment properly).
This commit is contained in:
Nick Gasson 2008-08-05 11:02:36 +01:00
parent c849dfeec4
commit e01e038cf9
2 changed files with 20 additions and 12 deletions
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30
tgt-vhdl/stmt.cc
View File

@ -81,11 +81,12 @@ static int draw_stask(vhdl_procedural *proc, stmt_container *container,
* the stmt_container class behaves like a Verilog block.
*/
static int draw_block(vhdl_procedural *proc, stmt_container *container,
ivl_statement_t stmt)
ivl_statement_t stmt, bool is_last)
{
int count = ivl_stmt_block_count(stmt);
for (int i = 0; i < count; i++) {
if (draw_stmt(proc, container, ivl_stmt_block_stmt(stmt, i)) != 0)
ivl_statement_t stmt_i = ivl_stmt_block_stmt(stmt, i);
if (draw_stmt(proc, container, stmt_i, is_last && i == count - 1) != 0)
return 1;
}
return 0;
@ -318,7 +319,7 @@ static int draw_nbassign(vhdl_procedural *proc, stmt_container *container,
}
static int draw_assign(vhdl_procedural *proc, stmt_container *container,
ivl_statement_t stmt)
ivl_statement_t stmt, bool is_last)
{
if (proc->get_scope()->allow_signal_assignment()) {
// Blocking assignment is implemented as non-blocking assignment
@ -326,9 +327,12 @@ static int draw_assign(vhdl_procedural *proc, stmt_container *container,
// This follows the Verilog semantics fairly closely.
make_assignment<vhdl_nbassign_stmt>(proc, container, stmt, false);
container->add_stmt
(new vhdl_wait_stmt(VHDL_WAIT_FOR, new vhdl_const_time(0)));
// Don't generate a zero-wait if this is the last statement in
// the process
if (!is_last)
container->add_stmt
(new vhdl_wait_stmt(VHDL_WAIT_FOR, new vhdl_const_time(0)));
}
else
make_assignment<vhdl_assign_stmt>(proc, container, stmt, true);
@ -422,7 +426,7 @@ static int draw_wait(vhdl_procedural *_proc, stmt_container *container,
}
}
draw_stmt(proc, container, ivl_stmt_sub_stmt(stmt));
draw_stmt(proc, container, ivl_stmt_sub_stmt(stmt), true);
container->add_stmt(wait);
}
else {
@ -462,7 +466,7 @@ static int draw_wait(vhdl_procedural *_proc, stmt_container *container,
}
container->add_stmt(new vhdl_wait_stmt(VHDL_WAIT_UNTIL, test));
draw_stmt(proc, container, ivl_stmt_sub_stmt(stmt));
draw_stmt(proc, container, ivl_stmt_sub_stmt(stmt), true);
}
return 0;
@ -609,9 +613,13 @@ int draw_repeat(vhdl_procedural *proc, stmt_container *container,
* add them to the given VHDL process. The container is the
* location to add statements: e.g. the process body, a branch
* of an if statement, etc.
*
* The flag is_last should be set if this is the final statement
* in a block or process. It avoids generating useless `wait for 0ns'
* statements if the next statement would be a wait anyway.
*/
int draw_stmt(vhdl_procedural *proc, stmt_container *container,
ivl_statement_t stmt)
ivl_statement_t stmt, bool is_last)
{
assert(stmt);
@ -619,11 +627,11 @@ int draw_stmt(vhdl_procedural *proc, stmt_container *container,
case IVL_ST_STASK:
return draw_stask(proc, container, stmt);
case IVL_ST_BLOCK:
return draw_block(proc, container, stmt);
return draw_block(proc, container, stmt, is_last);
case IVL_ST_NOOP:
return draw_noop(proc, container, stmt);
case IVL_ST_ASSIGN:
return draw_assign(proc, container, stmt);
return draw_assign(proc, container, stmt, is_last);
case IVL_ST_ASSIGN_NB:
return draw_nbassign(proc, container, stmt);
case IVL_ST_DELAY:

2
tgt-vhdl/vhdl_target.h
View File

@ -18,7 +18,7 @@ void error(const char *fmt, ...);
int draw_scope(ivl_scope_t scope, void *_parent);
int draw_process(ivl_process_t net, void *cd);
int draw_stmt(vhdl_procedural *proc, stmt_container *container,
ivl_statement_t stmt);
ivl_statement_t stmt, bool is_last = false);
int draw_lpm(vhdl_arch *arch, ivl_lpm_t lpm);
void draw_logic(vhdl_arch *arch, ivl_net_logic_t log);