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Canonicalize comparisons
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* fge x, y -> fle y, x
* fgt x, y -> flt y, x
* sge x, y -> sle y, x
* sgt x, y -> slt y, x
* uge x, y -> ule y, x
* ugt x, y -> ult y, x
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@kristerw
kristerw committed Oct 22, 2024
1 parent 8c75c06 commit 5f05381
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Showing 3 changed files with 140 additions and 167 deletions.
52 changes: 0 additions & 52 deletions lib/check.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -185,58 +185,6 @@ Inst *Converter::get_inst(const Cse_key& key, bool may_add_insts)
if (I != key2inst.end())
return I->second;
}
else if (inst_info[(int)key.op].iclass == Inst_class::icomparison
|| inst_info[(int)key.op].iclass == Inst_class::fcomparison)
{
Op op;
switch (key.op)
{
case Op::FGE:
op = Op::FLE;
break;
case Op::FGT:
op = Op::FLT;
break;
case Op::FLE:
op = Op::FGE;
break;
case Op::FLT:
op = Op::FGT;
break;
case Op::SGE:
op = Op::SLE;
break;
case Op::SGT:
op = Op::SLT;
break;
case Op::SLE:
op = Op::SGE;
break;
case Op::SLT:
op = Op::SGT;
break;
case Op::UGE:
op = Op::ULE;
break;
case Op::UGT:
op = Op::ULT;
break;
case Op::ULE:
op = Op::UGE;
break;
case Op::ULT:
op = Op::UGT;
break;
default:
throw Not_implemented("Converter::get_inst: unknown comparison");
}
Cse_key tmp_key = key;
tmp_key.op = op;
std::swap(tmp_key.arg1, tmp_key.arg2);
I = key2inst.find(tmp_key);
if (I != key2inst.end())
return I->second;
}

// Check if this is a negation of an existing comparison.
if (may_add_insts
Expand Down
215 changes: 120 additions & 95 deletions lib/simplify_insts.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1286,105 +1286,126 @@ bool is_ext(Inst *inst)
return false;
}

Inst *simplify_fge(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// fge x, y -> fle y, x
Inst *new_inst = create_inst(Op::FLE, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_fgt(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// fgt x, y -> flt y, x
Inst *new_inst = create_inst(Op::FLT, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_sge(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// sge x, x -> true
// sge x, y -> sle y, x
Inst *new_inst = create_inst(Op::SLE, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_sgt(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// sgt x, y -> slt y, x
Inst *new_inst = create_inst(Op::SLT, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_sle(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// sle x, x -> true
if (arg1 == arg2)
return inst->bb->value_inst(1, 1);

return inst;
}

Inst *simplify_sgt(Inst *inst)
Inst *simplify_slt(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// sgt signed_min_val, x -> false
if (is_value_signed_min(arg1))
// slt x, x -> false
if (arg1 == arg2)
return inst->bb->value_inst(0, 1);

// sgt x, signed_max_val -> false
if (is_value_signed_max(arg2))
// slt x, signed_min_val -> false
if (is_value_signed_min(arg2))
return inst->bb->value_inst(0, 1);

// For Boolean x: sgt (zext x), c -> false if c is a constant > 0.
// slt signed_max_val, x -> false
if (is_value_signed_max(arg1))
return inst->bb->value_inst(0, 1);

// For Boolean x: slt c, (zext x) -> false if c is a constant > 0.
// This is rather common in UB checks of range information where a Boolean
// has been extended to an integer.
if (arg1->op == Op::ZEXT
&& arg1->args[0]->bitsize == 1
&& arg2->op == Op::VALUE
&& arg2->signed_value() > 0)
if (arg2->op == Op::ZEXT
&& arg2->args[0]->bitsize == 1
&& arg1->op == Op::VALUE
&& arg1->signed_value() > 0)
return inst->bb->value_inst(0, 1);

// For Boolean x: sgt c, (zext x) -> false if c is a constant <= 0.
if (arg1->op == Op::VALUE
&& arg1->signed_value() <= 0
&& arg2->op == Op::ZEXT
&& arg2->args[0]->bitsize == 1)
// For Boolean x: slt (zext x), c -> false if c is a constant <= 0.
if (arg2->op == Op::VALUE
&& arg2->signed_value() <= 0
&& arg1->op == Op::ZEXT
&& arg1->args[0]->bitsize == 1)
return inst->bb->value_inst(0, 1);

// sgt c, (sext x) -> false if c <= the minimal possible value of x
if (arg1->op == Op::VALUE && arg2->op == Op::SEXT)
// slt (sext x), c -> false if c <= the minimal possible value of x
if (arg1->op == Op::SEXT && arg2->op == Op::VALUE)
{
__int128 min_val = 1;
min_val = min_val << 127;
min_val = min_val >> (128 - arg2->args[0]->bitsize);
if (arg1->signed_value() <= min_val)
min_val = min_val >> (128 - arg1->args[0]->bitsize);
if (arg2->signed_value() <= min_val)
return inst->bb->value_inst(0, 1);
}

// sgt (sext x), c -> false if c >= the maximal possible value of x
if (arg2->op == Op::VALUE
&& arg1->op == Op::SEXT
&& arg1->args[0]->bitsize > 1)
// slt c, (sext x) -> false if c >= the maximal possible value of x
if (arg1->op == Op::VALUE
&& arg2->op == Op::SEXT
&& arg2->args[0]->bitsize > 1)
{
unsigned __int128 max_val = -1;
max_val = max_val >> (129 - arg1->args[0]->bitsize);
if (arg2->signed_value() >= (__int128)max_val)
max_val = max_val >> (129 - arg2->args[0]->bitsize);
if (arg1->signed_value() >= (__int128)max_val)
return inst->bb->value_inst(0, 1);
}

// sgt 0, (zext x) -> false
if (is_value_zero(arg1) && arg2->op == Op::ZEXT)
// slt (zext x), 0 -> false
if (arg1->op == Op::ZEXT && is_value_zero(arg2))
return inst->bb->value_inst(0, 1);

// sgt (zext x), c -> false if c >= (zext -1)
if (arg1->bitsize <= 128
&& arg1->op == Op::ZEXT
&& arg2->op == Op::VALUE
&& arg2->signed_value() >= (((__int128)1 << arg1->args[0]->bitsize) - 1))
return inst->bb->value_inst(0, 1);

// sgt x, x -> false
if (arg1 == arg2)
return inst->bb->value_inst(0, 1);

return inst;
}

Inst *simplify_sle(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// sle x, x -> true
if (arg1 == arg2)
return inst->bb->value_inst(1, 1);

return inst;
}

Inst *simplify_slt(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// slt x, x -> false
if (arg1 == arg2)
// slt c, (zext x) -> false if c >= (zext -1)
if (arg2->bitsize <= 128
&& arg2->op == Op::ZEXT
&& arg1->op == Op::VALUE
&& arg1->signed_value() >= (((__int128)1 << arg2->args[0]->bitsize) - 1))
return inst->bb->value_inst(0, 1);

return inst;
Expand Down Expand Up @@ -1650,47 +1671,21 @@ Inst *simplify_uge(Inst *inst)
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// uge x, x -> true
if (arg1 == arg2)
return inst->bb->value_inst(1, 1);

return inst;
// uge x, y -> ule y, x
Inst *new_inst = create_inst(Op::ULE, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_ugt(Inst *inst)
{
Inst *const arg1 = inst->args[0];
Inst *const arg2 = inst->args[1];

// ugt 0, x -> false
if (is_value_zero(arg1))
return inst->bb->value_inst(0, 1);

// ugt x, -1 -> false
if (is_value_m1(arg2))
return inst->bb->value_inst(0, 1);

// ugt (zext x), c -> false if c >= the maximal possible value of x
if (arg1->op == Op::ZEXT
&& arg2->op == Op::VALUE)
{
unsigned __int128 max_val = -1;
max_val = max_val >> (128 - arg1->args[0]->bitsize);
if (arg2->value() >= max_val)
return inst->bb->value_inst(0, 1);
}

// ugt (and x, y), x -> false
// ugt (and x, y), y -> false
if (arg1->op == Op::AND
&& (arg1->args[0] == arg2 || arg1->args[1] == arg2))
return inst->bb->value_inst(0, 1);

// ugt x, x -> false
if (arg1 == arg2)
return inst->bb->value_inst(0, 1);

return inst;
// ugt x, y -> ult y, x
Inst *new_inst = create_inst(Op::ULT, arg2, arg1);
new_inst->insert_before(inst);
return new_inst;
}

Inst *simplify_ule(Inst *inst)
Expand All @@ -1714,6 +1709,30 @@ Inst *simplify_ult(Inst *inst)
if (arg1 == arg2)
return inst->bb->value_inst(0, 1);

// ult x, 0 -> false
if (is_value_zero(arg2))
return inst->bb->value_inst(0, 1);

// ult -1, x -> false
if (is_value_m1(arg1))
return inst->bb->value_inst(0, 1);

// ult (zext x), c -> false if c >= the maximal possible value of x
if (arg2->op == Op::ZEXT
&& arg1->op == Op::VALUE)
{
unsigned __int128 max_val = -1;
max_val = max_val >> (128 - arg2->args[0]->bitsize);
if (arg1->value() >= max_val)
return inst->bb->value_inst(0, 1);
}

// ult x, (and x, y) -> false
// ult y, (and x, y) -> false
if (arg2->op == Op::AND
&& (arg2->args[0] == arg1 || arg2->args[1] == arg1))
return inst->bb->value_inst(0, 1);

return inst;
}

Expand Down Expand Up @@ -2252,6 +2271,12 @@ Inst *simplify_inst(Inst *inst)
case Op::U2F:
inst = simplify_u2f(inst);
break;
case Op::FGE:
inst = simplify_fge(inst);
break;
case Op::FGT:
inst = simplify_fgt(inst);
break;
case Op::SEXT:
inst = simplify_sext(inst);
break;
Expand Down Expand Up @@ -2294,7 +2319,7 @@ Inst *simplify_inst(Inst *inst)
case Op::XOR:
inst = simplify_xor(inst);
break;
case Op:: ZEXT:
case Op::ZEXT:
inst = simplify_zext(inst);
break;
default:
Expand Down
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