Fix assertion failure in bitOpTree opt

[yTakatsukasa]

Second try to repair #2891

Ast such as below caused the issue:

     XOR 0x55aed9e5b430 <e104786#> {d70bs} @dt=0x55aed9c4e050@(G/wu32/1)
    1: CCAST 0x55aeda436a10 <e147374#> {d70bs} @dt=0x55aed9c4e050@(G/wu32/1) sz32
    1:1: SHIFTR 0x55aed9e5aec0 <e147371#> {d70bs} @dt=0x55aed9d80f80@(G/wu64/33)
    1:1:1: CCAST 0x55aed9e5af80 <e147361#> {d30cl} @dt=0x55aed9d80f80@(G/wu64/33) sz64
    1:1:1:1: WORDSEL 0x55aeda07ea30 <e336940#> {d30cn} @dt=0x55aed9c4d170@(G/w32)
    1:1:1:1:1: VARREF 0x55aeda435af0 <e147260#> {d30cn} @dt=0x55aed9c3ff20@(w128)p[3:0]  t__DOT__data_i [RV] <- VAR 0x55aed9e48c70 <e2223#> {d23aw} u4=0x1 @dt=0x55aed9c3ff20@(w128)p[3:0]  t__DOT__data_i [VSTATIC]  VAR
    1:1:1:1:2: CONST 0x55aeda07e0a0 <e147261#> {d30ct} @dt=0x55aed9c4d170@(G/w32)  32'h0
    1:1:2: CONST 0x55aed9e59d60 <e147362#> {d70bs} @dt=0x55aed9c4d170@(G/w32)  32'h20
    2: CCAST 0x55aeda436ad0 <e147394#> {d70bs} @dt=0x55aed9c4e050@(G/wu32/1) sz32
    2:1: SHIFTR 0x55aed9e5adf0 <e147391#> {d70bs} @dt=0x55aed9d80f80@(G/wu64/33)
    2:1:1: VARREF 0x55aed9e5a110 <e147381#> {d70bs} @dt=0x55aed9d80f80@(G/wu64/33)  t__DOT__genblk1__BRA__0__KET____DOT__u_bank_data_ecc_check__DOT____Vtogcov__data_i [LV] => VAR 0x55aed9f7dec0 <e27062#> {d70bs} @dt=0x55aed9c3d320@(G/w33)  t__DOT__genblk1__BRA__0__KET____DOT__u_bank_data_ecc_check__DOT____Vtogcov__data_i MODULETEMP

The bitwidth of a variable considering casts in tree requires traversing backp().
Instead of doing so, the width of m_bitPolarity is dynamically expanded if necessary.

I ran ext_tests with --trace and --coverage enabled.

[wsnyder]

What is the * 2 for? Below you are only initing up to width, not width*2.

[yTakatsukasa]

The code is expanding m_bitPolarity.
So newWidth must be greater than bit + 1.
Expanding to bit + 1 is maybe ok, but expanding by 2x is better because

• CCast will cast to such bitwidth anyway (33 bit width has to be 64 in C++)
• can avoid frequent expansion

The expanded m_bitPolarity is filled by 'X', then copy from oldPol .

verilator/src/V3Const.cpp

Lines 120 to 126 in 6af31c3

	m_bitPolarity.setAllBitsX();
	for (int i = 0; i < oldPol.width(); ++i) {
	if (oldPol.bitIs0(i))
	m_bitPolarity.setBit(i, '0');
	else if (oldPol.bitIs1(i))
	m_bitPolarity.setBit(i, '1');
	}

This is matches the initialization inf ctor.

verilator/src/V3Const.cpp

Lines 179 to 183 in 6af31c3

	VarInfo(ConstBitOpTreeVisitor* parent, AstVarRef* refp)
	: m_parentp(parent)
	, m_refp(refp)
	, m_bitPolarity(refp, refp->isWide() ? VL_EDATASIZE : refp->width()) {
	m_bitPolarity.setAllBitsX();

Thanks for highlighting this code. I noticed that m_bitPolarity has to be expanded more than 2x in some cases. (e.g. 8 to 32)
So I pushed 6af31c3.

[yTakatsukasa]

@wsnyder Does the comment above answer your question ?

[wsnyder]

Yes, thanks

[RaynardQiao]

With the latest master , All testcase passed. #2891
thanks