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JITDivGenerator.cpp
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/*
* Copyright (C) 2015-2019 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#
include
"
config.h
"
#
include
"
JITDivGenerator.h
"
#
if
ENABLE(JIT)
#
include
"
ArithProfile.h
"
#
include
"
JSCJSValueInlines.h
"
#
include
"
MathCommon.h
"
namespace
JSC
{
void
JITDivGenerator::loadOperand
(CCallHelpers& jit, SnippetOperand& opr, JSValueRegs oprRegs, FPRReg destFPR)
{
if
(opr.
isConstInt32
()) {
//
FIXME: this does not looks right.
//
-On x86_64, CVTSI2SD has partial register stall on its FPR.
//
A move or load might be a tiny bit larger but safer.
//
-On ARM64 we also have FMOV that can load small immediates.
jit.
move
(
CCallHelpers::Imm32
(opr.
asConstInt32
()), m_scratchGPR);
jit.
convertInt32ToDouble
(m_scratchGPR, destFPR);
}
else
if
(opr.
isConstDouble
()) {
jit.
move
(
CCallHelpers::Imm64
(opr.
asRawBits
()), m_scratchGPR);
jit.
move64ToDouble
(m_scratchGPR, destFPR);
}
else
{
if
(!opr.
definitelyIsNumber
())
m_slowPathJumpList.
append
(jit.
branchIfNotNumber
(oprRegs));
CCallHelpers::Jump notInt32 = jit.
branchIfNotInt32
(oprRegs);
jit.
convertInt32ToDouble
(oprRegs.
payloadGPR
(), destFPR);
CCallHelpers::Jump oprIsLoaded = jit.
jump
();
notInt32.
link
(&jit);
jit.
unboxDoubleNonDestructive
(oprRegs, destFPR, m_scratchGPR);
oprIsLoaded.
link
(&jit);
}
}
void
JITDivGenerator::generateFastPath
(CCallHelpers& jit)
{
ASSERT
(m_scratchGPR != InvalidGPRReg);
ASSERT
(m_scratchGPR != m_left.
payloadGPR
());
ASSERT
(m_scratchGPR != m_right.
payloadGPR
());
ASSERT
(!m_didEmitFastPath);
if
(!m_leftOperand.
mightBeNumber
() || !m_rightOperand.
mightBeNumber
())
return
;
ASSERT
(!m_leftOperand.
isConstInt32
() || !m_rightOperand.
isConstInt32
());
m_didEmitFastPath =
true
;
loadOperand
(jit, m_leftOperand, m_left, m_leftFPR);
std::optional<
double
> safeReciprocal;
if
(m_rightOperand.
isConst
()) {
double
constant = m_rightOperand.
asConstNumber
();
safeReciprocal =
safeReciprocalForDivByConst
(constant);
}
if
(safeReciprocal) {
jit.
move
(
CCallHelpers::Imm64
(std::bit_cast<
int64_t
>(*safeReciprocal)), m_scratchGPR);
jit.
move64ToDouble
(m_scratchGPR, m_rightFPR);
jit.
mulDouble
(m_rightFPR, m_leftFPR);
}
else
{
loadOperand
(jit, m_rightOperand, m_right, m_rightFPR);
jit.
divDouble
(m_rightFPR, m_leftFPR);
}
//
Is the result actually an integer? The DFG JIT would really like to know. If it's
//
not an integer, we set a bit. If this together with the slow case counter are below
//
threshold then the DFG JIT will compile this division with a speculation that the
//
remainder is zero.
//
As well, there are cases where a double result here would cause an important field
//
in the heap to sometimes have doubles in it, resulting in double predictions getting
//
propagated to a use site where it might cause damage (such as the index to an array
//
access). So if we are DFG compiling anything in the program, we want this code to
//
ensure that it produces integers whenever possible.
CCallHelpers::JumpList notInt32;
jit.
branchConvertDoubleToInt32
(m_leftFPR, m_scratchGPR, notInt32, m_scratchFPR);
//
If we've got an integer, we might as well make that the result of the division.
jit.
boxInt32
(m_scratchGPR, m_result);
m_endJumpList.
append
(jit.
jump
());
notInt32.
link
(&jit);
jit.
moveDoubleTo64
(m_leftFPR, m_scratchGPR);
CCallHelpers::Jump notDoubleZero = jit.
branchTest64
(CCallHelpers::NonZero, m_scratchGPR);
jit.
move
(GPRInfo::numberTagRegister, m_result.
payloadGPR
());
m_endJumpList.
append
(jit.
jump
());
notDoubleZero.
link
(&jit);
if
(m_arithProfile)
m_arithProfile->
emitUnconditionalSet
(jit, BinaryArithProfile::specialFastPathBit);
jit.
boxDouble
(m_leftFPR, m_result);
}
}
//
namespace JSC
#
endif
//
ENABLE(JIT)
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