/*
* optimizeExits does two conversions to eliminate common branch-to-exit flows.
*
* 1. If we see a jcc that leads to two "identical" blocks ending with
* bindjmp, then copy the identical part of the targets before the jcc,
* and replace the jcc with a bindjcc1st instruction using the bytecode
* destinations from the two original bindjmps. For the sake of this pass,
* "identical" means matching lea & syncvmsp instructions, and both bindjmp's
* are for the same function.
*
* This leads to more efficient code because the service request stubs will
* patch jumps in the main trace instead of off-trace.
*
* 2. Otherwise, if we see a jcc but only one of the branches is
* a normal exit, then convert the jcc to a bindexit with the jcc's condition
* and the original bindjmp's dest.
*/
void optimizeExits(Vunit& unit) {
auto const pred_counts = count_predecessors(unit);
PostorderWalker{unit} .dfs([&](Vlabel b) {
auto& code = unit.blocks[b].code;
assertx(!code.empty());
if (code.back().op != Vinstr::jcc) return;
auto const ijcc = code.back().jcc_;
auto const t0 = ijcc.targets[0];
auto const t1 = ijcc.targets[1];
if (t0 == t1) {
code.back() = jmp{t0};
return;
}
if (pred_counts[t0] != 1 || pred_counts[t1] != 1) return;
// copy all but the last instruction in blocks[t] to just before
// the last instruction in code.
auto hoist_sync = [&](Vlabel t) {
const auto& tcode = unit.blocks[t].code;
code.insert(std::prev(code.end()),
tcode.begin(), std::prev(tcode.end()));
};
if (match_bindjcc1st(unit, t0, t1)) {
// hoist the sync instructions from t0 to before the jcc,
// and replace the jcc with bindjcc1st.
const auto& bj0 = unit.blocks[t0].code.back().bindjmp_;
const auto& bj1 = unit.blocks[t1].code.back().bindjmp_;
hoist_sync(t0);
code.back() = bindjcc1st{ijcc.cc, ijcc.sf, {bj0.target, bj1.target},
bj0.args | bj1.args};
return;
}
auto fold_exit = [&](ConditionCode cc, Vlabel exit, Vlabel next) {
const auto& bj = unit.blocks[exit].code.back().bindjmp_;
auto origin = code.back().origin;
hoist_sync(exit);
code.back() = bindjcc{cc, ijcc.sf, bj.target, bj.trflags, bj.args};
code.emplace_back(jmp{next});
code.back().origin = origin;
};
// Try to replace jcc to normal exit with bindexit followed by jmp,
// as long as the sp adjustment is harmless to hoist (disp==0)
Vptr sp;
if (match_bindjmp(unit, t1, &sp) && sp == sp.base[0]) {
fold_exit(ijcc.cc, t1, t0);
} else if (match_bindjmp(unit, t0, &sp) && sp == sp.base[0]) {
fold_exit(ccNegate(ijcc.cc), t0, t1);
}
});
printUnit(kVasmExitsLevel, "after vasm-exits", unit);
}
void CodeGenerator::cgGuardStk(IRInstruction* inst) {
auto const rSP = x2a(curOpd(inst->src(0)).reg());
auto const baseOff = cellsToBytes(inst->extra<GuardStk>()->offset);
emitTypeTest(
inst->typeParam(),
rSP[baseOff + TVOFF(m_type)],
rSP[baseOff + TVOFF(m_data)],
[&] (ConditionCode cc) {
auto const destSK = SrcKey(curFunc(), m_unit.bcOff());
auto const destSR = m_tx64->getSrcRec(destSK);
destSR->emitFallbackJump(this->m_mainCode, ccNegate(cc));
});
}
void Vgen::emit(jcc i) {
assertx(i.cc != CC_None);
if (i.targets[1] != i.targets[0]) {
if (next == i.targets[1]) {
// the taken branch is the fall-through block, invert the branch.
i = jcc{ccNegate(i.cc), i.sf, {i.targets[1], i.targets[0]}};
}
jccs.push_back({a->frontier(), i.targets[1]});
// B.cond range is +/- 1MB but this uses BR
emitSmashableJcc(*codeBlock, env.meta, kEndOfTargetChain, i.cc);
}
emit(jmp{i.targets[0]});
}
void CodeGenerator::cgGuardLoc(IRInstruction* inst) {
auto const rFP = x2a(m_regs[inst->src(0)].reg());
auto const baseOff = localOffset(inst->extra<GuardLoc>()->locId);
emitTypeTest(
inst->typeParam(),
rFP[baseOff + TVOFF(m_type)],
rFP[baseOff + TVOFF(m_data)],
[&] (ConditionCode cc) {
auto const destSK = SrcKey(curFunc(), m_unit.bcOff());
auto const destSR = m_tx64->getSrcRec(destSK);
destSR->emitFallbackJump(this->m_mainCode, ccNegate(cc));
});
}
void CodeGenerator::cgSideExitGuardStk(IRInstruction* inst) {
auto const sp = x2a(curOpd(inst->src(0)).reg());
auto const extra = inst->extra<SideExitGuardStk>();
emitTypeTest(
inst->typeParam(),
sp[cellsToBytes(extra->checkedSlot) + TVOFF(m_type)],
sp[cellsToBytes(extra->checkedSlot) + TVOFF(m_data)],
[&] (ConditionCode cc) {
auto const sk = SrcKey(curFunc(), extra->taken);
emitBindSideExit(this->m_mainCode, this->m_stubsCode, sk, ccNegate(cc));
}
);
}
bool simplify(Env& env, const setcc& vsetcc, Vlabel b, size_t i) {
return if_inst<Vinstr::xorbi>(env, b, i + 1, [&] (const xorbi& vxorbi) {
// setcc{cc, _, tmp}; xorbi{1, tmp, d, _}; --> setcc{~cc, _, tmp};
if (!(env.use_counts[vsetcc.d] == 1 &&
vxorbi.s0.b() == 1 &&
vxorbi.s1 == vsetcc.d &&
env.use_counts[vxorbi.sf] == 0)) return false;
return simplify_impl(env, b, i, [&] (Vout& v) {
v << setcc{ccNegate(vsetcc.cc), vsetcc.sf, vxorbi.d};
return 2;
});
});
}
/*
* Branch fusion:
* Analyze blocks one at a time, looking for the sequence:
*
* setcc cc, f1 => b
* ...
* testb b, b => f2
* ...
* jcc E|NE, f2
*
* If found, and f2 is only used by the jcc, then change the code to:
*
* setcc cc, f1 => b
* ...
* nop
* ...
* jcc !cc|cc, f1
*
* Later, vasm-dead will clean up the nop, and the setcc if b became dead.
*
* During the search, any other instruction that has a status flag result
* will reset the pattern matcher. No instruction can "kill" flags,
* since flags are SSA variables. However the transformation we want to
* make extends the setcc flags lifetime, and we don't want it to overlap
* another flag's lifetime.
*/
void fuseBranches(Vunit& unit) {
auto blocks = sortBlocks(unit);
jit::vector<unsigned> uses(unit.next_vr);
for (auto b : blocks) {
for (auto& inst : unit.blocks[b].code) {
visitUses(unit, inst, [&](Vreg r) {
uses[r]++;
});
}
}
bool should_print = false;
for (auto b : blocks) {
auto& code = unit.blocks[b].code;
ConditionCode cc;
Vreg setcc_flags, setcc_dest, testb_flags;
unsigned testb_index;
for (unsigned i = 0, n = code.size(); i < n; ++i) {
if (code[i].op == Vinstr::setcc) {
cc = code[i].setcc_.cc;
setcc_flags = code[i].setcc_.sf;
setcc_dest = code[i].setcc_.d;
continue;
}
if (setcc_flags.isValid() &&
match_testb(code[i], setcc_dest) &&
uses[code[i].testb_.sf] == 1) {
testb_flags = code[i].testb_.sf;
testb_index = i;
continue;
}
if (match_jcc(code[i], testb_flags)) {
code[testb_index] = nop{}; // erase the testb
auto& jcc = code[i].jcc_;
jcc.cc = jcc.cc == CC_NE ? cc : ccNegate(cc);
jcc.sf = setcc_flags;
should_print = true;
continue;
}
if (setcc_flags.isValid() && sets_flags(code[i])) {
setcc_flags = testb_flags = Vreg{};
}
}
}
if (should_print) {
printUnit(kVasmFusionLevel, "after vasm-fusion", unit);
}
}
bool cmov_impl(Env& env, const Inst& inst, Vlabel b, size_t i, Extend extend) {
auto const t_it = env.unit.regToConst.find(inst.t);
if (t_it == env.unit.regToConst.end()) return false;
auto const f_it = env.unit.regToConst.find(inst.f);
if (f_it == env.unit.regToConst.end()) return false;
auto const check_const = [](Vconst c, bool& val) {
if (c.isUndef) return false;
switch (c.kind) {
case Vconst::Quad:
case Vconst::Long:
case Vconst::Byte:
if (c.val == 0) {
val = false;
return true;
} else if (c.val == 1) {
val = true;
return true;
} else {
return false;
}
case Vconst::Double:
return false;
}
not_reached();
};
bool t_val;
if (!check_const(t_it->second, t_val)) return false;
bool f_val;
if (!check_const(f_it->second, f_val)) return false;
return simplify_impl(
env, b, i, [&] (Vout& v) {
auto const d = env.unit.makeReg();
if (t_val == f_val) {
v << copy{env.unit.makeConst(t_val), d};
} else if (t_val) {
v << setcc{inst.cc, inst.sf, d};
} else {
v << setcc{ccNegate(inst.cc), inst.sf, d};
}
extend(v, d, inst.d);
return 1;
}
);
}
void optimizeJmps(Vunit& unit) {
auto isEmpty = [&](Vlabel b, Vinstr::Opcode op) {
auto& code = unit.blocks[b].code;
return code.size() == 1 && op == code[0].op;
};
bool changed = false;
bool ever_changed = false;
// The number of incoming edges from (reachable) predecessors for each block.
// It is maintained as an upper bound of the actual value during the
// transformation.
jit::vector<int> npreds(unit.blocks.size(), 0);
do {
if (changed) {
std::fill(begin(npreds), end(npreds), 0);
}
changed = false;
PostorderWalker{unit} .dfs([&](Vlabel b) {
for (auto s : succs(unit.blocks[b])) {
npreds[s]++;
}
});
// give entry an extra predecessor to prevent cloning it.
npreds[unit.entry]++;
PostorderWalker{unit} .dfs([&](Vlabel b) {
auto& block = unit.blocks[b];
auto& code = block.code;
assertx(!code.empty());
if (code.back().op == Vinstr::jcc) {
auto ss = succs(block);
if (ss[0] == ss[1]) {
// both edges have same target, change to jmp
code.back() = jmp{ss[0]};
--npreds[ss[0]];
changed = true;
} else {
auto jcc_i = code.back().jcc_;
if (isEmpty(jcc_i.targets[0], Vinstr::fallback)) {
jcc_i = jcc{ccNegate(jcc_i.cc), jcc_i.sf,
{jcc_i.targets[1], jcc_i.targets[0]}};
}
if (isEmpty(jcc_i.targets[1], Vinstr::fallback)) {
// replace jcc with fallbackcc and jmp
const auto& fb_i = unit.blocks[jcc_i.targets[1]].code[0].fallback_;
const auto t0 = jcc_i.targets[0];
const auto jcc_origin = code.back().origin;
code.pop_back();
code.emplace_back(
fallbackcc{jcc_i.cc, jcc_i.sf, fb_i.dest, fb_i.trflags});
code.back().origin = jcc_origin;
code.emplace_back(jmp{t0});
code.back().origin = jcc_origin;
changed = true;
}
}
}
for (auto& s : succs(block)) {
if (isEmpty(s, Vinstr::jmp)) {
// skip over s
--npreds[s];
s = unit.blocks[s].code.back().jmp_.target;
++npreds[s];
changed = true;
}
}
if (code.back().op == Vinstr::jmp) {
auto s = code.back().jmp_.target;
if (npreds[s] == 1 || isEmpty(s, Vinstr::jcc)) {
// overwrite jmp with copy of s
auto& code2 = unit.blocks[s].code;
code.pop_back();
code.insert(code.end(), code2.begin(), code2.end());
if (--npreds[s]) {
for (auto ss : succs(block)) {
++npreds[ss];
}
}
changed = true;
}
}
});
ever_changed |= changed;
} while (changed);
if (ever_changed) {
printUnit(kVasmJumpsLevel, "after vasm-jumps", unit);
}
}
void cgCheckType(IRLS& env, const IRInstruction* inst) {
// Note: If you add new supported type checks, you should update
// negativeCheckType() to indicate whether it is precise or not.
auto const src = inst->src(0);
auto const dst = inst->dst();
auto const srcData = srcLoc(env, inst, 0).reg(0);
auto const srcType = srcLoc(env, inst, 0).reg(1);
auto& v = vmain(env);
auto const doJcc = [&] (ConditionCode cc, Vreg sf) {
fwdJcc(v, env, ccNegate(cc), sf, inst->taken());
};
auto const doMov = [&] {
auto const dstData = dstLoc(env, inst, 0).reg(0);
auto const dstType = dstLoc(env, inst, 0).reg(1);
if (dst->isA(TBool) && !src->isA(TBool)) {
v << movtqb{srcData, dstData};
} else {
v << copy{srcData, dstData};
}
if (dstType == InvalidReg) return;
if (srcType != InvalidReg) {
v << copy{srcType, dstType};
} else {
v << ldimmq{src->type().toDataType(), dstType};
}
};
auto const typeParam = inst->typeParam();
if (src->isA(typeParam)) {
// src is the target type or better. Just define our dst.
doMov();
return;
}
if (!src->type().maybe(typeParam)) {
// src is definitely not the target type. Always jump.
v << jmp{label(env, inst->taken())};
return;
}
if (srcType != InvalidReg) {
emitTypeTest(v, env, typeParam, srcType, srcData, v.makeReg(), doJcc);
doMov();
return;
}
if (src->type() <= TBoxedCell && typeParam <= TBoxedCell) {
// We should never have specific known Boxed types; those should only be
// used for hints and predictions.
always_assert(!(typeParam < TBoxedInitCell));
doMov();
return;
}
/*
* See if we're just checking the array kind or object class of a value with
* a mostly-known type.
*
* Important: We don't support typeParam being something like
* StaticArr=kPackedKind unless the src->type() also already knows its
* staticness. We do allow things like CheckType<Arr=Packed> t1:StaticArr,
* though. This is why we have to check that the unspecialized type is at
* least as big as the src->type().
*/
if (typeParam.isSpecialized() &&
typeParam.unspecialize() >= src->type()) {
detail::emitSpecializedTypeTest(v, env, typeParam, srcData,
v.makeReg(), doJcc);
doMov();
return;
}
/*
* Since not all of our unions carry a type register, there are some
* situations with strings and arrays that are neither constantly-foldable
* nor in the emitTypeTest() code path.
*
* We currently actually check their persistent bit here, which will let
* both static and uncounted strings through. Also note that
* CheckType<Uncounted> t1:{Null|Str} doesn't get this treatment currently---
* the emitTypeTest() path above will only check the type register.
*/
if (!typeParam.isSpecialized() &&
typeParam <= TUncounted &&
src->type().subtypeOfAny(TStr, TArr) &&
src->type().maybe(typeParam)) {
assertx(src->type().maybe(TPersistent));
auto const sf = v.makeReg();
v << cmplim{0, srcData[FAST_REFCOUNT_OFFSET], sf};
doJcc(CC_L, sf);
doMov();
return;
}
always_assert_flog(
false,
"Bad src: {} and dst: {} types in '{}'",
src->type(), typeParam, *inst
);
}
