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machinst x64: adapt conversions for saturation behaviors;

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This commit is contained in:
Benjamin Bouvier
2020-07-22 16:46:12 +02:00
parent cd54f05efd
commit e43310a088
3 changed files with 223 additions and 119 deletions
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177
cranelift/codegen/src/isa/x64/inst/emit.rs
View File

@@ -1672,7 +1672,7 @@ pub(crate) fn emit(
// mov %src, %tmp_gpr2
// and $1, %tmp_gpr2
// or %tmp_gpr1, %tmp_gpr2
// ctsi2sd/cvtsi2ss %tmp_gpr2, %dst
// cvtsi2sd/cvtsi2ss %tmp_gpr2, %dst
// addsd/addss %dst, %dst
//
// done:
@@ -1769,25 +1769,45 @@ pub(crate) fn emit(
Inst::CvtFloatToSintSeq {
src_size,
dst_size,
is_saturating,
src,
dst,
tmp_gpr,
tmp_xmm,
srcloc,
} => {
// Emits the following sequence:
// Emits the following common sequence:
//
// cvttss2si/cvttsd2si %src, %dst
// cmp $INT_MIN, %dst ;; 2 instructions (movaps + reg cmp) for 64-bits ints
// jnz done
// cmp %dst, 1
// jno done
//
// Then, for saturating conversions:
//
// ;; check for NaN
// cmpss/cmpsd %src, %src
// jnp check_if_correct
// jnp not_nan
// xor %dst, %dst
//
// ;; positive inputs get saturated to INT_MAX; negative ones to INT_MIN, which is
// ;; already in %dst.
// mov 0, %tmp_gpr
// movd/movq %tmp_gpr, %tmp_xmm
// cmpss/cmpsd %src, %tmp_xmm
// jnb done
// mov/movaps $INT_MAX, %dst
//
// done:
//
// Then, for non-saturating conversions:
//
// ;; check for NaN
// cmpss/cmpsd %src, %src
// jnp not_nan
// ud2 trap BadConversionToInteger
//
// ;; check if INT_MIN was the correct result, against a magic constant:
// check_if_correct:
// not_nan:
// movaps/mov $magic, %tmp_gpr
// movq/movd %tmp_gpr, %tmp_xmm
// cmpss/cmpsd %tmp_xmm, %src
@@ -1812,32 +1832,64 @@ pub(crate) fn emit(
};
let done = sink.get_label();
let not_nan = sink.get_label();
// The truncation.
let inst = Inst::xmm_to_gpr(trunc_op, src, *dst, *dst_size);
inst.emit(sink, flags, state);
// Generate constant INT_MIN, and compare against it.
if *dst_size == OperandSize::Size64 {
let inst = Inst::imm_r(true, 0x8000000000000000, *tmp_gpr);
// Compare against 1, in case of overflow the dst operand was INT_MIN.
let inst = Inst::cmp_rmi_r(dst_size.to_bytes(), RegMemImm::imm(1), dst.to_reg());
inst.emit(sink, flags, state);
let inst = Inst::cmp_rmi_r(8, RegMemImm::reg(tmp_gpr.to_reg()), dst.to_reg());
inst.emit(sink, flags, state);
} else {
// Emit a simple comparison.
let inst = Inst::cmp_rmi_r(4, RegMemImm::imm(0x80000000), dst.to_reg());
inst.emit(sink, flags, state);
}
one_way_jmp(sink, CC::NZ, done); // == (int)
one_way_jmp(sink, CC::NO, done); // no overflow => done
// Check for NaN.
let inst = Inst::xmm_cmp_rm_r(cmp_op, RegMem::reg(src), src);
inst.emit(sink, flags, state);
let check_if_correct = sink.get_label();
one_way_jmp(sink, CC::NP, check_if_correct); // jump over trap if not a NaN
one_way_jmp(sink, CC::NP, not_nan); // go to not_nan if not a NaN
if *is_saturating {
// For NaN, emit 0.
let inst = Inst::alu_rmi_r(
*dst_size == OperandSize::Size64,
AluRmiROpcode::Xor,
RegMemImm::reg(dst.to_reg()),
*dst,
);
inst.emit(sink, flags, state);
let inst = Inst::jmp_known(BranchTarget::Label(done));
inst.emit(sink, flags, state);
sink.bind_label(not_nan);
// If the input was positive, saturate to INT_MAX.
// TODO use xorps/xorpd here
let inst = Inst::imm_r(false, 0, *tmp_gpr); // rely on sign-extension to get 0 on 64-bits
inst.emit(sink, flags, state);
let inst =
Inst::gpr_to_xmm(cast_op, RegMem::reg(tmp_gpr.to_reg()), *src_size, *tmp_xmm);
inst.emit(sink, flags, state);
let inst = Inst::xmm_cmp_rm_r(cmp_op, RegMem::reg(src), tmp_xmm.to_reg());
inst.emit(sink, flags, state);
// Jump if >= to done.
one_way_jmp(sink, CC::NB, done);
// Otherwise, put INT_MAX.
if *dst_size == OperandSize::Size64 {
let inst = Inst::imm_r(true, 0x7fffffffffffffff, *dst);
inst.emit(sink, flags, state);
} else {
let inst = Inst::imm_r(false, 0x7fffffff, *dst);
inst.emit(sink, flags, state);
}
} else {
let check_positive = sink.get_label();
let inst = Inst::trap(*srcloc, TrapCode::BadConversionToInteger);
inst.emit(sink, flags, state);
@@ -1848,7 +1900,7 @@ pub(crate) fn emit(
// If the src register is less (or in some cases, less-or-equal) than the threshold,
// trap!
sink.bind_label(check_if_correct);
sink.bind_label(not_nan);
let mut no_overflow_cc = CC::NB; // >=
let output_bits = dst_size.to_bits();
@@ -1859,8 +1911,8 @@ pub(crate) fn emit(
inst.emit(sink, flags, state);
}
OperandSize::Size64 => {
// An f64 can represent `i32::min_value() - 1` exactly with precision to spare, so
// there are values less than -2^(N-1) that convert correctly to INT_MIN.
// An f64 can represent `i32::min_value() - 1` exactly with precision to spare,
// so there are values less than -2^(N-1) that convert correctly to INT_MIN.
let cst = if output_bits < 64 {
no_overflow_cc = CC::NBE; // >
Ieee64::fcvt_to_sint_negative_overflow(output_bits)
@@ -1879,8 +1931,8 @@ pub(crate) fn emit(
let inst = Inst::xmm_cmp_rm_r(cmp_op, RegMem::reg(tmp_xmm.to_reg()), src);
inst.emit(sink, flags, state);
let check_positive = sink.get_label();
one_way_jmp(sink, no_overflow_cc, check_positive); // jump over trap if src >= or > threshold
// jump over trap if src >= or > threshold
one_way_jmp(sink, no_overflow_cc, check_positive);
let inst = Inst::trap(*srcloc, TrapCode::IntegerOverflow);
inst.emit(sink, flags, state);
@@ -1904,6 +1956,7 @@ pub(crate) fn emit(
let inst = Inst::trap(*srcloc, TrapCode::IntegerOverflow);
inst.emit(sink, flags, state);
}
sink.bind_label(done);
}
@@ -1911,13 +1964,15 @@ pub(crate) fn emit(
Inst::CvtFloatToUintSeq {
src_size,
dst_size,
is_saturating,
src,
dst,
tmp_gpr,
tmp_xmm,
srcloc,
} => {
// Emits the following sequence:
// The only difference in behavior between saturating and non-saturating is how we
// handle errors. Emits the following sequence:
//
// movaps/mov 2**(int_width - 1), %tmp_gpr
// movq/movd %tmp_gpr, %tmp_xmm
@@ -1925,21 +1980,24 @@ pub(crate) fn emit(
// jnb is_large
//
// ;; check for NaN inputs
// jnp next
// ud2 trap BadConversionToInteger
// jnp not_nan
// -- non-saturating: ud2 trap BadConversionToInteger
// -- saturating: xor %dst, %dst; j done
//
// next:
// not_nan:
// cvttss2si/cvttsd2si %src, %dst
// cmp 0, %dst
// jnl done
// ud2 trap IntegerOverflow
// -- non-saturating: ud2 trap IntegerOverflow
// -- saturating: xor %dst, %dst; j done
//
// is_large:
// subss/subsd %tmp_xmm, %src ; <-- we clobber %src here
// cvttss2si/cvttss2sd %tmp_x, %dst
// cmp 0, %dst
// jnl next_is_large
// ud2 trap IntegerOverflow
// -- non-saturating: ud2 trap IntegerOverflow
// -- saturating: movaps $UINT_MAX, %dst; j done
//
// next_is_large:
// add 2**(int_width -1), %dst ;; 2 instructions for 64-bits integers
@@ -1986,13 +2044,28 @@ pub(crate) fn emit(
let handle_large = sink.get_label();
one_way_jmp(sink, CC::NB, handle_large); // jump to handle_large if src >= large_threshold
let next = sink.get_label();
one_way_jmp(sink, CC::NP, next); // jump over trap if not NaN
let not_nan = sink.get_label();
one_way_jmp(sink, CC::NP, not_nan); // jump over trap if not NaN
let inst = Inst::trap(*srcloc, TrapCode::BadConversionToInteger);
if *is_saturating {
// Emit 0.
let inst = Inst::alu_rmi_r(
*dst_size == OperandSize::Size64,
AluRmiROpcode::Xor,
RegMemImm::reg(dst.to_reg()),
*dst,
);
inst.emit(sink, flags, state);
sink.bind_label(next);
let inst = Inst::jmp_known(BranchTarget::Label(done));
inst.emit(sink, flags, state);
} else {
// Trap.
let inst = Inst::trap(*srcloc, TrapCode::BadConversionToInteger);
inst.emit(sink, flags, state);
}
sink.bind_label(not_nan);
// Actual truncation for small inputs: if the result is not positive, then we had an
// overflow.
@@ -2005,8 +2078,24 @@ pub(crate) fn emit(
one_way_jmp(sink, CC::NL, done); // if dst >= 0, jump to done
if *is_saturating {
// The input was "small" (< 2**(width -1)), so the only way to get an integer
// overflow is because the input was too small: saturate to the min value, i.e. 0.
let inst = Inst::alu_rmi_r(
*dst_size == OperandSize::Size64,
AluRmiROpcode::Xor,
RegMemImm::reg(dst.to_reg()),
*dst,
);
inst.emit(sink, flags, state);
let inst = Inst::jmp_known(BranchTarget::Label(done));
inst.emit(sink, flags, state);
} else {
// Trap.
let inst = Inst::trap(*srcloc, TrapCode::IntegerOverflow);
inst.emit(sink, flags, state);
}
// Now handle large inputs.
@@ -2024,8 +2113,26 @@ pub(crate) fn emit(
let next_is_large = sink.get_label();
one_way_jmp(sink, CC::NL, next_is_large); // if dst >= 0, jump to next_is_large
if *is_saturating {
// The input was "large" (>= 2**(width -1)), so the only way to get an integer
// overflow is because the input was too large: saturate to the max value.
let inst = Inst::imm_r(
true,
if *dst_size == OperandSize::Size64 {
u64::max_value()
} else {
u32::max_value() as u64
},
*dst,
);
inst.emit(sink, flags, state);
let inst = Inst::jmp_known(BranchTarget::Label(done));
inst.emit(sink, flags, state);
} else {
let inst = Inst::trap(*srcloc, TrapCode::IntegerOverflow);
inst.emit(sink, flags, state);
}
sink.bind_label(next_is_large);

31
cranelift/codegen/src/isa/x64/inst/mod.rs
View File

@@ -250,6 +250,7 @@ pub enum Inst {
CvtFloatToSintSeq {
dst_size: OperandSize,
src_size: OperandSize,
is_saturating: bool,
/// A copy of the source register, fed by lowering. It is marked as modified during
/// register allocation to make sure that the temporary xmm register differs from the src
/// register, since both registers are live at the same time in the generated code
@@ -265,6 +266,7 @@ pub enum Inst {
CvtFloatToUintSeq {
src_size: OperandSize,
dst_size: OperandSize,
is_saturating: bool,
/// A copy of the source register, fed by lowering, reused as a temporary. It is marked as
/// modified during register allocation to make sure that the temporary xmm register
/// differs from the src register, since both registers are live at the same time in the
@@ -578,10 +580,11 @@ impl Inst {
pub(crate) fn cvt_float_to_sint_seq(
src_size: OperandSize,
dst_size: OperandSize,
is_saturating: bool,
src: Writable<Reg>,
dst: Writable<Reg>,
tmp_xmm: Writable<Reg>,
tmp_gpr: Writable<Reg>,
tmp_xmm: Writable<Reg>,
srcloc: SourceLoc,
) -> Inst {
debug_assert!(src.to_reg().get_class() == RegClass::V128);
@@ -589,10 +592,11 @@ impl Inst {
debug_assert!(tmp_gpr.to_reg().get_class() == RegClass::I64);
debug_assert!(dst.to_reg().get_class() == RegClass::I64);
Inst::CvtFloatToSintSeq {
src,
dst,
src_size,
dst_size,
is_saturating,
src,
dst,
tmp_gpr,
tmp_xmm,
srcloc,
@@ -602,6 +606,7 @@ impl Inst {
pub(crate) fn cvt_float_to_uint_seq(
src_size: OperandSize,
dst_size: OperandSize,
is_saturating: bool,
src: Writable<Reg>,
dst: Writable<Reg>,
tmp_gpr: Writable<Reg>,
@@ -610,12 +615,14 @@ impl Inst {
) -> Inst {
debug_assert!(src.to_reg().get_class() == RegClass::V128);
debug_assert!(tmp_xmm.to_reg().get_class() == RegClass::V128);
debug_assert!(tmp_gpr.to_reg().get_class() == RegClass::I64);
debug_assert!(dst.to_reg().get_class() == RegClass::I64);
Inst::CvtFloatToUintSeq {
src,
dst,
src_size,
dst_size,
is_saturating,
src,
dst,
tmp_gpr,
tmp_xmm,
srcloc,
@@ -1363,13 +1370,8 @@ fn x64_get_regs(inst: &Inst, collector: &mut RegUsageCollector) {
tmp_xmm,
tmp_gpr,
..
} => {
collector.add_mod(*src);
collector.add_def(*dst);
collector.add_def(*tmp_xmm);
collector.add_def(*tmp_gpr);
}
Inst::CvtFloatToUintSeq {
| Inst::CvtFloatToUintSeq {
src,
dst,
tmp_gpr,
@@ -1633,13 +1635,8 @@ fn x64_map_regs<RUM: RegUsageMapper>(inst: &mut Inst, mapper: &RUM) {
ref mut tmp_xmm,
ref mut tmp_gpr,
..
} => {
map_mod(mapper, src);
map_def(mapper, dst);
map_def(mapper, tmp_xmm);
map_def(mapper, tmp_gpr);
}
Inst::CvtFloatToUintSeq {
| Inst::CvtFloatToUintSeq {
ref mut src,
ref mut dst,
ref mut tmp_gpr,

16
cranelift/codegen/src/isa/x64/lower.rs
View File

@@ -1016,7 +1016,7 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
};
}
Opcode::FcvtToUint | Opcode::FcvtToSint => {
Opcode::FcvtToUint | Opcode::FcvtToUintSat | Opcode::FcvtToSint | Opcode::FcvtToSintSat => {
let src = input_to_reg(ctx, inputs[0]);
let dst = output_to_reg(ctx, outputs[0]);
@@ -1036,23 +1036,23 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
OperandSize::Size64
};
let to_signed = op == Opcode::FcvtToSint;
let to_signed = op == Opcode::FcvtToSint || op == Opcode::FcvtToSintSat;
let is_sat = op == Opcode::FcvtToUintSat || op == Opcode::FcvtToSintSat;
let src_copy = ctx.alloc_tmp(RegClass::V128, input_ty);
ctx.emit(Inst::gen_move(src_copy, src, input_ty));
let tmp_xmm = ctx.alloc_tmp(RegClass::V128, input_ty);
let tmp_gpr = ctx.alloc_tmp(RegClass::I64, output_ty);
let srcloc = ctx.srcloc(insn);
if to_signed {
let tmp_xmm = ctx.alloc_tmp(RegClass::V128, input_ty);
let tmp_gpr = ctx.alloc_tmp(RegClass::I64, output_ty);
ctx.emit(Inst::cvt_float_to_sint_seq(
src_size, dst_size, src_copy, dst, tmp_xmm, tmp_gpr, srcloc,
src_size, dst_size, is_sat, src_copy, dst, tmp_gpr, tmp_xmm, srcloc,
));
} else {
let tmp_xmm = ctx.alloc_tmp(RegClass::V128, input_ty);
let tmp_gpr = ctx.alloc_tmp(RegClass::I64, output_ty);
ctx.emit(Inst::cvt_float_to_uint_seq(
src_size, dst_size, src_copy, dst, tmp_gpr, tmp_xmm, srcloc,
src_size, dst_size, is_sat, src_copy, dst, tmp_gpr, tmp_xmm, srcloc,
));
}
}