user1132959
Reputation: 988
How to tell the compiler not to optimize variables used in inline assembly?
I'm having some trouble getting my code working when compiled with optimizations and with inline assembly.
I don't believe it would help for me to actually post the assembly because this is a more general question.
My inline assembly uses the same variables as the C version(passed as input parameters)
asm ( "" : : "r" (arg1), "r" (arg2) :);
My question is, how can I get the compiler to not optimize these variables? The functionality only breaks for assembly when compiled with optimizations. I have tried volatile, but it's still not acting right.
Thanks.
Update:
I'm trying to implement NEON optimizations for OpenCV, specifically the lkpyramid.cpp file. The problem is, in release mode (where optimizations are set) it does not work properly. However, in debug mode, it works fine. I tracked down a specific variable(FLT_SCALE) that was being optimized out and made it volatile and that part worked fine after that, but I'm still having incorrect behavior from another optimization.
The gcc version could vary since this is an open source project, but the one I'm currently using is 4.8.1. The target architecture is ARMv7 w/ NEON. The processor I'm testing on is an ARM Cortex-A15(big.LITTLE).
Below is my code at its current state. Ignore all the comments and volatiles(for testing this problem) everywhere. It's WIP. I removed unrelated code so I could fit it in here. I think the problem is in the bottom most asm block because if I do if(false) to skip it, I don't run into the problem. Thanks.
#include "precomp.hpp"
#include <float.h>
#include <stdio.h>
#include "lkpyramid.hpp"
namespace
{
static void calcSharrDeriv(const cv::Mat& src, cv::Mat& dst)
{
using namespace cv;
using cv::detail::deriv_type;
int rows = src.rows, cols = src.cols, cn = src.channels(), colsn = cols*cn, depth = src.depth();
CV_Assert(depth == CV_8U);
dst.create(rows, cols, CV_MAKETYPE(DataType<deriv_type>::depth, cn*2));
#ifdef HAVE_TEGRA_OPTIMIZATION
if (tegra::calcSharrDeriv(src, dst))
return;
#endif
int x, y, delta = (int)alignSize((cols + 2)*cn, 16);
AutoBuffer<deriv_type> _tempBuf(delta*2 + 64);
deriv_type *trow0 = alignPtr(_tempBuf + cn, 16), *trow1 = alignPtr(trow0 + delta, 16);
int three = 3, ten = 10;
for( y = 0; y < rows; y++ )
{
const uchar* srow0 = src.ptr<uchar>(y > 0 ? y-1 : rows > 1 ? 1 : 0);
const uchar* srow1 = src.ptr<uchar>(y);
const uchar* srow2 = src.ptr<uchar>(y < rows-1 ? y+1 : rows > 1 ? rows-2 : 0);
deriv_type* drow = dst.ptr<deriv_type>(y);
// do vertical convolution
x = 0;
#ifdef CV_NEON
//assumes deriv_type is 16 bits
if(sizeof(deriv_type) == 2 && colsn >= 16)
{
__asm__ volatile ( "vdup.16 q8, %0\n\t"
"vdup.8 d18, %1\n\t"
:
: "r" (three), "r" (ten)
: );
for( ; x <= colsn - 8; x += 8)
{
__asm__ volatile ( "vld1.8 {d0}, [%0]\n\t"
"vld1.8 {d1}, [%1]\n\t"
"vld1.8 {d2}, [%2]\n\t"
"vaddl.u8 q4, d0, d2\n\t"
"vsubl.u8 q11, d2, d0\n\t"
"vmul.u16 q5, q4, q8\n\t"
"vmull.u8 q6, d1, d18\n\t"
"vadd.u16 q10, q6, q5\n\t"
"vst1.16 {q10}, [%3]\n\t"
"vst1.16 {q11}, [%4]\n\t"
:
: "r" (srow0 + x),
"r" (srow1 + x),
"r" (srow2 + x),
"r" (trow0 + x),
"r" (trow1 + x)
:
);
}
}
#endif
for( ; x < colsn; x++ )
{
int t0 = (srow0[x] + srow2[x])*3 + srow1[x]*10;
int t1 = srow2[x] - srow0[x];
trow0[x] = (deriv_type)t0;
trow1[x] = (deriv_type)t1;
}
// make border
int x0 = (cols > 1 ? 1 : 0)*cn, x1 = (cols > 1 ? cols-2 : 0)*cn;
for( int k = 0; k < cn; k++ )
{
trow0[-cn + k] = trow0[x0 + k]; trow0[colsn + k] = trow0[x1 + k];
trow1[-cn + k] = trow1[x0 + k]; trow1[colsn + k] = trow1[x1 + k];
}
#ifdef CV_NEON
__asm__ volatile ( "vdup.16 q8, %0\n\t"
"vdup.16 q9, %1\n\t"
:
: "r" (three), "r" (ten)
: );
#endif
// do horizontal convolution, interleave the results and store them to dst
x = 0;
#ifdef CV_NEON
//assumes size of deriv_type is 16 bits
if(sizeof(deriv_type) == 2 && colsn >= 16)
{
for( ; x <= colsn - 8; x += 8 )
{
__asm__ volatile (
"vld1.16 {q0}, [%0]\n\t" //trow0[x + cn]
"vld1.16 {q1}, [%1]\n\t" //trow0[x - cn]
"vsub.i16 q5, q0, q1\n\t" //this is t0
"vld1.16 {q2}, [%2]\n\t" //trow1[x + cn]
"vld1.16 {q3}, [%3]\n\t" //trow1[x - cn]
"vadd.i16 q6, q2, q3\n\t" //this needs mult by 3
"vld1.16 {q4}, [%4]\n\t" //trow1[x]
"vmul.i16 q7, q6, q8\n\t" //this needs to add to trow1[x]*10
"vmul.i16 q10, q4, q9\n\t" //this is trow1[x]*10
"vadd.i16 q11, q7, q10\n\t" //this is t1
"vswp d22, d11\n\t"
"vst2.16 {q5}, [%5]\n\t" //interleave
"vst2.16 {q11}, [%6]\n\t" //interleave
:
: "r" (trow0 + x + cn), //0
"r" (trow0 + x - cn), //1
"r" (trow1 + x + cn), //2
"r" (trow1 + x - cn), //3
"r" (trow1 + x), //4
"r" (drow + (x*2)), //5
"r" (drow + (x*2)+8) //6
:
);
}
}
#endif
for( ; x < colsn; x++ )
{
deriv_type t0 = (deriv_type)(trow0[x+cn] - trow0[x-cn]);
deriv_type t1 = (deriv_type)((trow1[x+cn] + trow1[x-cn])*3 + trow1[x]*10);
drow[x*2] = t0; drow[x*2+1] = t1;
}
}
}
}//namespace
cv::detail::LKTrackerInvoker::LKTrackerInvoker(
const Mat& _prevImg, const Mat& _prevDeriv, const Mat& _nextImg,
const Point2f* _prevPts, Point2f* _nextPts,
uchar* _status, float* _err,
Size _winSize, TermCriteria _criteria,
int _level, int _maxLevel, int _flags, float _minEigThreshold )
{
prevImg = &_prevImg;
prevDeriv = &_prevDeriv;
nextImg = &_nextImg;
prevPts = _prevPts;
nextPts = _nextPts;
status = _status;
err = _err;
winSize = _winSize;
criteria = _criteria;
level = _level;
maxLevel = _maxLevel;
flags = _flags;
minEigThreshold = _minEigThreshold;
}
void cv::detail::LKTrackerInvoker::operator()(const Range& range) const
{
Point2f halfWin((winSize.width-1)*0.5f, (winSize.height-1)*0.5f);
const Mat& I = *prevImg;
const Mat& J = *nextImg;
const Mat& derivI = *prevDeriv;
int j, cn = I.channels(), cn2 = cn*2;
cv::AutoBuffer<deriv_type> _buf(winSize.area()*(cn + cn2));
int derivDepth = DataType<deriv_type>::depth;
Mat IWinBuf(winSize, CV_MAKETYPE(derivDepth, cn), (deriv_type*)_buf);
Mat derivIWinBuf(winSize, CV_MAKETYPE(derivDepth, cn2), (deriv_type*)_buf + winSize.area()*cn);
for( int ptidx = range.start; ptidx < range.end; ptidx++ )
{
Point2f prevPt = prevPts[ptidx]*(float)(1./(1 << level));
Point2f nextPt;
if( level == maxLevel )
{
if( flags & OPTFLOW_USE_INITIAL_FLOW )
nextPt = nextPts[ptidx]*(float)(1./(1 << level));
else
nextPt = prevPt;
}
else
nextPt = nextPts[ptidx]*2.f;
nextPts[ptidx] = nextPt;
Point2i iprevPt, inextPt;
prevPt -= halfWin;
iprevPt.x = cvFloor(prevPt.x);
iprevPt.y = cvFloor(prevPt.y);
if( iprevPt.x < -winSize.width || iprevPt.x >= derivI.cols ||
iprevPt.y < -winSize.height || iprevPt.y >= derivI.rows )
{
if( level == 0 )
{
if( status )
status[ptidx] = false;
if( err )
err[ptidx] = 0;
}
continue;
}
volatile float a = prevPt.x - iprevPt.x;
volatile float b = prevPt.y - iprevPt.y;
volatile const int W_BITS = 14, W_BITS1 = 14;
volatile const float FLT_SCALE = 1.f/(1 << 20); //volatile is needed because compiler will optimize this out for NEON
volatile int iw00 = cvRound((1.f - a)*(1.f - b)*(1 << W_BITS));
volatile int iw01 = cvRound(a*(1.f - b)*(1 << W_BITS));
volatile int iw10 = cvRound((1.f - a)*b*(1 << W_BITS));
volatile int iw11 = (1 << W_BITS) - iw00 - iw01 - iw10;
volatile int dstep = (int)(derivI.step/derivI.elemSize1());
volatile int stepI = (int)(I.step/I.elemSize1());
volatile int stepJ = (int)(J.step/J.elemSize1());
volatile float A11 = 0, A12 = 0, A22 = 0;
#ifdef CV_NEON
volatile int CV_DECL_ALIGNED(16) nA11[] = {0, 0, 0, 0}, nA12[] = {0, 0, 0, 0}, nA22[] = {0, 0, 0, 0};
volatile const int shifter1 = -(W_BITS - 5); //negative so it shifts right
volatile const int shifter2 = -(W_BITS);
if(sizeof(deriv_type) == 2)
{
__asm__ volatile ( "vdup.16 d26, %0\n\t"
"vdup.16 d27, %1\n\t"
"vdup.16 d28, %2\n\t"
"vdup.16 d29, %3\n\t"
"vdup.32 q11, %4\n\t"
"vdup.32 q12, %5\n\t"
:
: "r" ((short)iw00),
"r" ((short)iw01),
"r" ((short)iw10),
"r" ((short)iw11),
"r" (shifter1),
"r" (shifter2)
: );
}
#endif
// extract the patch from the first image, compute covariation matrix of derivatives
volatile int x, y;
for( y = 0; y < winSize.height; y++ )
{
volatile const uchar* src = (const uchar*)I.data + (y + iprevPt.y)*stepI + iprevPt.x*cn;
volatile const deriv_type* dsrc = (const deriv_type*)derivI.data + (y + iprevPt.y)*dstep + iprevPt.x*cn2;
volatile deriv_type* Iptr = (deriv_type*)(IWinBuf.data + y*IWinBuf.step);
volatile deriv_type* dIptr = (deriv_type*)(derivIWinBuf.data + y*derivIWinBuf.step);
x = 0;
#ifdef CV_NEON
if(sizeof(deriv_type) == 2 && winSize.width*cn >= 12)
{
for( ; x <= winSize.width*cn - 4; x += 4, dsrc += 4*2, dIptr += 4*2 )
{
__asm__ volatile (
"vld1.8 {d0}, [%0]\n\t" //ignores last 4 bytes
"vmovl.u8 q0, d0\n\t" //expand to 16-bit
"vld1.8 {d2}, [%1]\n\t"
"vmovl.u8 q1, d2\n\t"
"vmull.s16 q5, d0, d26\n\t"
"vmull.s16 q6, d2, d27\n\t"
"vld1.8 {d4}, [%2]\n\t"
"vmovl.u8 q2, d4\n\t" //expand
"vld1.8 {d6}, [%3]\n\t"
"vmovl.u8 q3, d6\n\t"
"vmull.s16 q7, d4, d28\n\t"
"vmull.s16 q8, d6, d29\n\t"
"vadd.i32 q5, q5, q6\n\t"
"vadd.i32 q7, q7, q8\n\t"
"vadd.i32 q5, q5, q7\n\t"
"vld2.16 {d0, d1}, [%4]\n\t" //evens in d0 and d2
"vld2.16 {d2, d3}, [%5]\n\t"
"vqrshl.s32 q5, q5, q11\n\t"
"vmull.s16 q4, d0, d26\n\t" //q4 is mult of even 1
"vmull.s16 q6, d1, d26\n\t" //q6 is mult of odd 1
"vmovn.s32 d0, q5\n\t"
"vmull.s16 q7, d2, d27\n\t" //q7 is mult of even 2
"vmull.s16 q8, d3, d27\n\t" //q8 is mult of odd 2
"vst1.16 {d0}, [%8]\n\t"
"vld2.16 {d4, d5}, [%6]\n\t" //evens in d4 and d6
"vld2.16 {d6, d7}, [%7]\n\t"
"vadd.i32 q4, q4, q7\n\t" //this frees up q7 and q8
"vadd.i32 q6, q6, q8\n\t" //q4 is added even 1 and 2
//q6 is added odd 1 and 2
"vmull.s16 q7, d4, d28\n\t" //q7 is mult of even 3
"vmull.s16 q0, d5, d28\n\t" //q0 is mult of odd 3
"vmull.s16 q8, d6, d29\n\t" //q8 is mult of even 4
"vmull.s16 q15, d7, d29\n\t" //q15 is mult of odd 4
"vadd.i32 q7, q7, q8\n\t" //q7 is added even 3 and 4
"vadd.i32 q0, q0, q15\n\t" //q0 is added odd 3 and 4
"vadd.i32 q4, q4, q7\n\t" //q4 is added even 1,2,3,4 -- will be ixval
"vadd.i32 q6, q6, q0\n\t" //q6 is added odd 1,2,3,4 -- will be iyval
"vld1.32 {q1}, [%11]\n\t"
"vld1.32 {q2}, [%12]\n\t"
"vld1.32 {q0}, [%10]\n\t" //get the loads prepared
"vqrshl.s32 q4, q4, q12\n\t" //q4 is descaled evens added
"vqrshl.s32 q6, q6, q12\n\t" //q6 is descaled odds added
//now ixval is stored in q4 and iyval is stored in q6 and ival is in q5
"vmul.s32 q7, q4, q4\n\t"
"vmul.s32 q8, q4, q6\n\t"
"vmul.s32 q15, q6, q6\n\t"
"vadd.i32 q0, q0, q7\n\t"
"vadd.i32 q1, q1, q8\n\t"
"vadd.i32 q2, q2, q15\n\t"
"vst1.32 {q0}, [%10]\n\t"
"vst1.32 {q1}, [%11]\n\t"
"vst1.32 {q2}, [%12]\n\t"
"vmovn.i32 d8, q4\n\t" //bring ixval to short
"vmovn.i32 d12, q6\n\t" //bring iyval to short
"vswp d9, d12\n\t" //now d8 is ixval and d9 is iyval
"vst2.16 {d8, d9}, [%9]\n\t"
:
: "r" (src + x), //0
"r" (src + x + cn), //1
"r" (src + x + stepI), //2
"r" (src + x + stepI + cn), //3
"r" (dsrc), //4
"r" (dsrc + cn2), //5
"r" (dsrc + dstep), //6
"r" (dsrc + dstep + cn2), //7
"r" (Iptr + x), //8
"r" (dIptr), //9
"r" (nA11), //10
"r" (nA12), //11
"r" (nA22) //12
: );
}
}
#endif
for( ; x < winSize.width*cn; x++, dsrc += 2, dIptr += 2 )
{
int ival = CV_DESCALE(src[x]*iw00 + src[x+cn]*iw01 +
src[x+stepI]*iw10 + src[x+stepI+cn]*iw11, W_BITS1-5);
int ixval = CV_DESCALE(dsrc[0]*iw00 + dsrc[cn2]*iw01 +
dsrc[dstep]*iw10 + dsrc[dstep+cn2]*iw11, W_BITS1);
int iyval = CV_DESCALE(dsrc[1]*iw00 + dsrc[cn2+1]*iw01 + dsrc[dstep+1]*iw10 +
dsrc[dstep+cn2+1]*iw11, W_BITS1);
Iptr[x] = (short)ival;
dIptr[0] = (short)ixval;
dIptr[1] = (short)iyval;
A11 += (float)(ixval*ixval);
A12 += (float)(ixval*iyval);
A22 += (float)(iyval*iyval);
}
}
#ifdef CV_NEON
A11 += (float)(nA11[0] + nA11[1] + nA11[2] + nA11[3]);
A12 += (float)(nA12[0] + nA12[1] + nA12[2] + nA12[3]);
A22 += (float)(nA22[0] + nA22[1] + nA22[2] + nA22[3]);
#endif
A11 *= FLT_SCALE;
A12 *= FLT_SCALE;
A22 *= FLT_SCALE;
volatile float D = A11*A22 - A12*A12;
float minEig = (A22 + A11 - std::sqrt((A11-A22)*(A11-A22) +
4.f*A12*A12))/(2*winSize.width*winSize.height);
if( err && (flags & CV_LKFLOW_GET_MIN_EIGENVALS) != 0 )
err[ptidx] = (float)minEig;
if( minEig < minEigThreshold || D < FLT_EPSILON )
{
if( level == 0 && status )
status[ptidx] = false;
continue;
}
D = 1.f/D;
nextPt -= halfWin;
Point2f prevDelta;
for( j = 0; j < criteria.maxCount; j++ )
{
inextPt.x = cvFloor(nextPt.x);
inextPt.y = cvFloor(nextPt.y);
if( inextPt.x < -winSize.width || inextPt.x >= J.cols ||
inextPt.y < -winSize.height || inextPt.y >= J.rows )
{
if( level == 0 && status )
status[ptidx] = false;
break;
}
a = nextPt.x - inextPt.x;
b = nextPt.y - inextPt.y;
iw00 = cvRound((1.f - a)*(1.f - b)*(1 << W_BITS));
iw01 = cvRound(a*(1.f - b)*(1 << W_BITS));
iw10 = cvRound((1.f - a)*b*(1 << W_BITS));
iw11 = (1 << W_BITS) - iw00 - iw01 - iw10;
float b1 = 0, b2 = 0;
for( y = 0; y < winSize.height; y++ )
{
const uchar* Jptr = (const uchar*)J.data + (y + inextPt.y)*stepJ + inextPt.x*cn;
const deriv_type* Iptr = (const deriv_type*)(IWinBuf.data + y*IWinBuf.step);
const deriv_type* dIptr = (const deriv_type*)(derivIWinBuf.data + y*derivIWinBuf.step);
x = 0;
for( ; x < winSize.width*cn; x++, dIptr += 2 )
{
int diff = CV_DESCALE(Jptr[x]*iw00 + Jptr[x+cn]*iw01 +
Jptr[x+stepJ]*iw10 + Jptr[x+stepJ+cn]*iw11,
W_BITS1-5) - Iptr[x];
b1 += (float)(diff*dIptr[0]);
b2 += (float)(diff*dIptr[1]);
}
}
b1 *= FLT_SCALE;
b2 *= FLT_SCALE;
Point2f delta( (float)((A12*b2 - A22*b1) * D),
(float)((A12*b1 - A11*b2) * D));
//delta = -delta;
nextPt += delta;
nextPts[ptidx] = nextPt + halfWin;
if( delta.ddot(delta) <= criteria.epsilon )
break;
if( j > 0 && std::abs(delta.x + prevDelta.x) < 0.01 &&
std::abs(delta.y + prevDelta.y) < 0.01 )
{
nextPts[ptidx] -= delta*0.5f;
break;
}
prevDelta = delta;
}
if( status[ptidx] && err && level == 0 && (flags & CV_LKFLOW_GET_MIN_EIGENVALS) == 0 )
{
Point2f nextPoint = nextPts[ptidx] - halfWin;
Point inextPoint;
inextPoint.x = cvFloor(nextPoint.x);
inextPoint.y = cvFloor(nextPoint.y);
if( inextPoint.x < -winSize.width || inextPoint.x >= J.cols ||
inextPoint.y < -winSize.height || inextPoint.y >= J.rows )
{
if( status )
status[ptidx] = false;
continue;
}
float aa = nextPoint.x - inextPoint.x;
float bb = nextPoint.y - inextPoint.y;
iw00 = cvRound((1.f - aa)*(1.f - bb)*(1 << W_BITS));
iw01 = cvRound(aa*(1.f - bb)*(1 << W_BITS));
iw10 = cvRound((1.f - aa)*bb*(1 << W_BITS));
iw11 = (1 << W_BITS) - iw00 - iw01 - iw10;
float errval = 0.f;
for( y = 0; y < winSize.height; y++ )
{
const uchar* Jptr = (const uchar*)J.data + (y + inextPoint.y)*stepJ + inextPoint.x*cn;
const deriv_type* Iptr = (const deriv_type*)(IWinBuf.data + y*IWinBuf.step);
for( x = 0; x < winSize.width*cn; x++ )
{
int diff = CV_DESCALE(Jptr[x]*iw00 + Jptr[x+cn]*iw01 +
Jptr[x+stepJ]*iw10 + Jptr[x+stepJ+cn]*iw11,
W_BITS1-5) - Iptr[x];
errval += std::abs((float)diff);
}
}
err[ptidx] = errval * 1.f/(32*winSize.width*cn*winSize.height);
}
}
}
Upvotes: 1
Views: 1489
Answers (2)
user1132959
Reputation: 988
Corrected
With the help of the GCC mailing list. I found that, for one, I needed to add the registers used to the clobber list. Additionally, I had to do one of two things:
- Add "memory" to the clobber list, or
- To avoid flushing all memory, add "=m" (*((MemContainer128*)nA11)) where nA11 is some pointer and MemContainer128 is typedef struct { char x[16]; } MemContainer128; (16 is the length of the data in bytes) , to the output operands(even though I never reference it). Somehow it lets the compiler know that memory at that address will change, so reload it.
Thanks to Basile for the suggestion and also everyone who commented.
Upvotes: 0
Basile Starynkevitch
Reputation: 1
Read carefully the extended asm section of GCC documentation.
Please tell us more about the version of GCC you are using, the target processor, and the real asm instruction....
You may want asm volatile or asm goto
You could declare these variables as volatile, maybe
{ volatile auto varg1 = arg1;
volatile auto varg2 = arg2;
volatile asm ("" : : "r" (varg1), "r" (varg2) :);
}
And you should use a recent version of GCC, e.g. GCC 4.8 (today, in Feb. 2014) and in a few weeks the upcoming GCC 4.9
Perhaps [email protected] is a better place to ask.
Upvotes: 2
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