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Fix invalid optimisations in tgt-vvp. 

The vvp code generator was optimising away adds and subtracts where one
operand was a constant zero. This is not valid for 4-state arithmetic.
It was also optimising away multiplies by a constant zero - but in this
case getting it wrong and effectively multiplying by 1.
This commit is contained in:
Martin Whitaker 2014-02-28 23:29:15 +00:00
parent 065c48527c
commit c61d2151c1
1 changed files with 1 additions and 11 deletions
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12
tgt-vvp/eval_expr.c
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2001-2013 Stephen Williams (steve@icarus.com)
* Copyright (c) 2001-2014 Stephen Williams (steve@icarus.com)
*
* This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU
@ -1490,12 +1490,6 @@ static struct vector_info draw_add_immediate(ivl_expr_t le,
assert(number_is_immediate(re, IMM_WID, 0));
imm = get_number_immediate(re);
/* This shouldn't generally happen, because the elaborator
should take care of simple constant propagation like this,
but it doesn't have to and it is easy to catch here. */
if (imm == 0)
return lv;
switch (lv.base) {
case 0: /* Left expression is 0. */
lv.base = allocate_vector(wid);
@ -1556,8 +1550,6 @@ static struct vector_info draw_sub_immediate(ivl_expr_t le,
assert(! number_is_unknown(re));
assert(number_is_immediate(re, IMM_WID, 0));
imm = get_number_immediate(re);
if (imm == 0)
return lv;
switch (lv.base) {
case 0:
@ -1602,8 +1594,6 @@ static struct vector_info draw_mul_immediate(ivl_expr_t le,
assert(! number_is_unknown(re));
assert(number_is_immediate(re, IMM_WID, 0));
imm = get_number_immediate(re);
if (imm == 0)
return lv;
fprintf(vvp_out, " %%muli %u, %lu, %u;\n", lv.base, imm, lv.wid);