>Submitter-Id: net >Originator: Matteo Frigo >Organization: lost during childhood >Confidential: no >Synopsis: A case where -fnew-ra seriously degrades performance >Severity: serious >Priority: low >Category: optimization >Class: pessimizes-code >Release: 3.3 (Debian) (Debian testing/unstable) >Environment: System: Linux glauke 2.4.20 #1 Tue Apr 8 17:47:23 EDT 2003 ppc GNU/Linux Architecture: ppc
host: powerpc-unknown-linux-gnu build: powerpc-unknown-linux-gnu target: powerpc-unknown-linux-gnu configured with: ../src/configure -v --enable-languages=c,c++,java,f77,pascal,objc,ada --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc --disable-multilib powerpc-linux >Description: -fnew-ra seriously degrades the performance of FFTW, a Fourier transform library. (See www.fftw.org.) As an example, I have included below a code sample test.c, which computes the FFT of 32 complex numbers. (This program is a simplified version of the code from FFTW.) I compiled the test program on both a powerpc and an x86 machine. For the included test program, ``-O -fnew-ra'' produces substantially larger code than ``-O'' alone. (I am using ``-O'' instead of ``-O2'' in order to disable the first-pass instruction scheduler, which introduces even more register pressure.) RESULTS ON MACHINE 1 (powerpc-linux): glauke$ uname -a Linux glauke 2.4.20 #1 Tue Apr 8 17:47:23 EDT 2003 ppc GNU/Linux glauke$ gcc --version gcc (GCC) 3.3 (Debian) Copyright (C) 2003 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. glauke$ gcc -c -O test.c && size test.o text data bss dec hex filename 3024 0 0 3024 bd0 test.o glauke$ gcc -c -O -fnew-ra test.c && size test.o text data bss dec hex filename 5232 0 0 5232 1470 test.o RESULTS ON MACHINE 2 (i686-linux): [EMAIL PROTECTED]:/tmp$ uname -a Linux amd 2.4.20-1-k7 #1 Sat Mar 22 15:17:52 EST 2003 i686 GNU/Linux [EMAIL PROTECTED]:/tmp$ gcc --version gcc (GCC) 3.3 (Debian) Copyright (C) 2003 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. [EMAIL PROTECTED]:/tmp$ gcc -c -O test.c && size test.o text data bss dec hex filename 4218 0 0 4218 107a test.o [EMAIL PROTECTED]:/tmp$ gcc -c -O -fnew-ra test.c && size test.o text data bss dec hex filename 13601 0 0 13601 3521 test.o Thanks for your time and for developing gcc. Cheers, Matteo Frigo ------------------------------------------------------------ /* BEGIN test.c */ typedef double R; typedef R E; #define K(x) ((E) x) #define DK(name, value) const E name = K(value) #define FMA(a, b, c) (((a) * (b)) + (c)) #define FMS(a, b, c) (((a) * (b)) - (c)) #define FNMA(a, b, c) (- (((a) * (b)) + (c))) #define FNMS(a, b, c) ((c) - ((a) * (b))) #define R double #define E double /* * This function contains 372 FP additions, 84 FP multiplications, * (or, 340 additions, 52 multiplications, 32 fused multiply/add), * 99 stack variables, and 128 memory accesses */ void fft32(const R *ri, const R *ii, R *ro, R *io) { DK(KP831469612, +0.831469612302545237078788377617905756738560812); DK(KP555570233, +0.555570233019602224742830813948532874374937191); DK(KP195090322, +0.195090322016128267848284868477022240927691618); DK(KP980785280, +0.980785280403230449126182236134239036973933731); DK(KP923879532, +0.923879532511286756128183189396788286822416626); DK(KP382683432, +0.382683432365089771728459984030398866761344562); DK(KP707106781, +0.707106781186547524400844362104849039284835938); { E T7, T4r, T4Z, T18, T1z, T3t, T3T, T2T, Te, T1f, T50, T4s, T2W, T3u, T1G; E T3U, Tm, T1n, T1O, T2Z, T3y, T3X, T4w, T53, Tt, T1u, T1V, T2Y, T3B, T3W; E T4z, T52, T2t, T3L, T3O, T2K, TR, TY, T5F, T5G, T5H, T5I, T4R, T5j, T2E; E T3P, T4W, T5k, T2N, T3M, T22, T3E, T3H, T2j, TC, TJ, T5A, T5B, T5C, T5D; E T4G, T5g, T2d, T3F, T4L, T5h, T2m, T3I; { E T3, T1x, T14, T2S, T6, T2R, T17, T1y; { E T1, T2, T12, T13; T1 = ri[0]; T2 = ri[(2 * 16)]; T3 = T1 + T2; T1x = T1 - T2; T12 = ii[0]; T13 = ii[(2 * 16)]; T14 = T12 + T13; T2S = T12 - T13; } { E T4, T5, T15, T16; T4 = ri[(2 * 8)]; T5 = ri[(2 * 24)]; T6 = T4 + T5; T2R = T4 - T5; T15 = ii[(2 * 8)]; T16 = ii[(2 * 24)]; T17 = T15 + T16; T1y = T15 - T16; } T7 = T3 + T6; T4r = T3 - T6; T4Z = T14 - T17; T18 = T14 + T17; T1z = T1x - T1y; T3t = T1x + T1y; T3T = T2S - T2R; T2T = T2R + T2S; } { E Ta, T1B, T1b, T1A, Td, T1D, T1e, T1E; { E T8, T9, T19, T1a; T8 = ri[(2 * 4)]; T9 = ri[(2 * 20)]; Ta = T8 + T9; T1B = T8 - T9; T19 = ii[(2 * 4)]; T1a = ii[(2 * 20)]; T1b = T19 + T1a; T1A = T19 - T1a; } { E Tb, Tc, T1c, T1d; Tb = ri[(2 * 28)]; Tc = ri[(2 * 12)]; Td = Tb + Tc; T1D = Tb - Tc; T1c = ii[(2 * 28)]; T1d = ii[(2 * 12)]; T1e = T1c + T1d; T1E = T1c - T1d; } Te = Ta + Td; T1f = T1b + T1e; T50 = Td - Ta; T4s = T1b - T1e; { E T2U, T2V, T1C, T1F; T2U = T1D - T1E; T2V = T1B + T1A; T2W = KP707106781 * (T2U - T2V); T3u = KP707106781 * (T2V + T2U); T1C = T1A - T1B; T1F = T1D + T1E; T1G = KP707106781 * (T1C - T1F); T3U = KP707106781 * (T1C + T1F); } } { E Ti, T1L, T1j, T1J, Tl, T1I, T1m, T1M, T1K, T1N; { E Tg, Th, T1h, T1i; Tg = ri[(2 * 2)]; Th = ri[(2 * 18)]; Ti = Tg + Th; T1L = Tg - Th; T1h = ii[(2 * 2)]; T1i = ii[(2 * 18)]; T1j = T1h + T1i; T1J = T1h - T1i; } { E Tj, Tk, T1k, T1l; Tj = ri[(2 * 10)]; Tk = ri[(2 * 26)]; Tl = Tj + Tk; T1I = Tj - Tk; T1k = ii[(2 * 10)]; T1l = ii[(2 * 26)]; T1m = T1k + T1l; T1M = T1k - T1l; } Tm = Ti + Tl; T1n = T1j + T1m; T1K = T1I + T1J; T1N = T1L - T1M; T1O = FNMS(KP923879532, T1N, KP382683432 * T1K); T2Z = FMA(KP923879532, T1K, KP382683432 * T1N); { E T3w, T3x, T4u, T4v; T3w = T1J - T1I; T3x = T1L + T1M; T3y = FNMS(KP382683432, T3x, KP923879532 * T3w); T3X = FMA(KP382683432, T3w, KP923879532 * T3x); T4u = T1j - T1m; T4v = Ti - Tl; T4w = T4u - T4v; T53 = T4v + T4u; } } { E Tp, T1S, T1q, T1Q, Ts, T1P, T1t, T1T, T1R, T1U; { E Tn, To, T1o, T1p; Tn = ri[(2 * 30)]; To = ri[(2 * 14)]; Tp = Tn + To; T1S = Tn - To; T1o = ii[(2 * 30)]; T1p = ii[(2 * 14)]; T1q = T1o + T1p; T1Q = T1o - T1p; } { E Tq, Tr, T1r, T1s; Tq = ri[(2 * 6)]; Tr = ri[(2 * 22)]; Ts = Tq + Tr; T1P = Tq - Tr; T1r = ii[(2 * 6)]; T1s = ii[(2 * 22)]; T1t = T1r + T1s; T1T = T1r - T1s; } Tt = Tp + Ts; T1u = T1q + T1t; T1R = T1P + T1Q; T1U = T1S - T1T; T1V = FMA(KP382683432, T1R, KP923879532 * T1U); T2Y = FNMS(KP923879532, T1R, KP382683432 * T1U); { E T3z, T3A, T4x, T4y; T3z = T1Q - T1P; T3A = T1S + T1T; T3B = FMA(KP923879532, T3z, KP382683432 * T3A); T3W = FNMS(KP382683432, T3z, KP923879532 * T3A); T4x = Tp - Ts; T4y = T1q - T1t; T4z = T4x + T4y; T52 = T4x - T4y; } } { E TN, T2p, T2J, T4S, TQ, T2G, T2s, T4T, TU, T2x, T2w, T4O, TX, T2z, T2C; E T4P; { E TL, TM, T2H, T2I; TL = ri[(2 * 31)]; TM = ri[(2 * 15)]; TN = TL + TM; T2p = TL - TM; T2H = ii[(2 * 31)]; T2I = ii[(2 * 15)]; T2J = T2H - T2I; T4S = T2H + T2I; } { E TO, TP, T2q, T2r; TO = ri[(2 * 7)]; TP = ri[(2 * 23)]; TQ = TO + TP; T2G = TO - TP; T2q = ii[(2 * 7)]; T2r = ii[(2 * 23)]; T2s = T2q - T2r; T4T = T2q + T2r; } { E TS, TT, T2u, T2v; TS = ri[(2 * 3)]; TT = ri[(2 * 19)]; TU = TS + TT; T2x = TS - TT; T2u = ii[(2 * 3)]; T2v = ii[(2 * 19)]; T2w = T2u - T2v; T4O = T2u + T2v; } { E TV, TW, T2A, T2B; TV = ri[(2 * 27)]; TW = ri[(2 * 11)]; TX = TV + TW; T2z = TV - TW; T2A = ii[(2 * 27)]; T2B = ii[(2 * 11)]; T2C = T2A - T2B; T4P = T2A + T2B; } T2t = T2p - T2s; T3L = T2p + T2s; T3O = T2J - T2G; T2K = T2G + T2J; TR = TN + TQ; TY = TU + TX; T5F = TR - TY; { E T4N, T4Q, T2y, T2D; T5G = T4S + T4T; T5H = T4O + T4P; T5I = T5G - T5H; T4N = TN - TQ; T4Q = T4O - T4P; T4R = T4N - T4Q; T5j = T4N + T4Q; T2y = T2w - T2x; T2D = T2z + T2C; T2E = KP707106781 * (T2y - T2D); T3P = KP707106781 * (T2y + T2D); { E T4U, T4V, T2L, T2M; T4U = T4S - T4T; T4V = TX - TU; T4W = T4U - T4V; T5k = T4V + T4U; T2L = T2z - T2C; T2M = T2x + T2w; T2N = KP707106781 * (T2L - T2M); T3M = KP707106781 * (T2M + T2L); } } } { E Ty, T2f, T21, T4C, TB, T1Y, T2i, T4D, TF, T28, T2b, T4I, TI, T23, T26; E T4J; { E Tw, Tx, T1Z, T20; Tw = ri[(2 * 1)]; Tx = ri[(2 * 17)]; Ty = Tw + Tx; T2f = Tw - Tx; T1Z = ii[(2 * 1)]; T20 = ii[(2 * 17)]; T21 = T1Z - T20; T4C = T1Z + T20; } { E Tz, TA, T2g, T2h; Tz = ri[(2 * 9)]; TA = ri[(2 * 25)]; TB = Tz + TA; T1Y = Tz - TA; T2g = ii[(2 * 9)]; T2h = ii[(2 * 25)]; T2i = T2g - T2h; T4D = T2g + T2h; } { E TD, TE, T29, T2a; TD = ri[(2 * 5)]; TE = ri[(2 * 21)]; TF = TD + TE; T28 = TD - TE; T29 = ii[(2 * 5)]; T2a = ii[(2 * 21)]; T2b = T29 - T2a; T4I = T29 + T2a; } { E TG, TH, T24, T25; TG = ri[(2 * 29)]; TH = ri[(2 * 13)]; TI = TG + TH; T23 = TG - TH; T24 = ii[(2 * 29)]; T25 = ii[(2 * 13)]; T26 = T24 - T25; T4J = T24 + T25; } T22 = T1Y + T21; T3E = T2f + T2i; T3H = T21 - T1Y; T2j = T2f - T2i; TC = Ty + TB; TJ = TF + TI; T5A = TC - TJ; { E T4E, T4F, T27, T2c; T5B = T4C + T4D; T5C = T4I + T4J; T5D = T5B - T5C; T4E = T4C - T4D; T4F = TI - TF; T4G = T4E - T4F; T5g = T4F + T4E; T27 = T23 - T26; T2c = T28 + T2b; T2d = KP707106781 * (T27 - T2c); T3F = KP707106781 * (T2c + T27); { E T4H, T4K, T2k, T2l; T4H = Ty - TB; T4K = T4I - T4J; T4L = T4H - T4K; T5h = T4H + T4K; T2k = T2b - T28; T2l = T23 + T26; T2m = KP707106781 * (T2k - T2l); T3I = KP707106781 * (T2k + T2l); } } } { E T4B, T57, T5a, T5c, T4Y, T56, T55, T5b; { E T4t, T4A, T58, T59; T4t = T4r - T4s; T4A = KP707106781 * (T4w - T4z); T4B = T4t + T4A; T57 = T4t - T4A; T58 = FNMS(KP923879532, T4L, KP382683432 * T4G); T59 = FMA(KP382683432, T4W, KP923879532 * T4R); T5a = T58 - T59; T5c = T58 + T59; } { E T4M, T4X, T51, T54; T4M = FMA(KP923879532, T4G, KP382683432 * T4L); T4X = FNMS(KP923879532, T4W, KP382683432 * T4R); T4Y = T4M + T4X; T56 = T4X - T4M; T51 = T4Z - T50; T54 = KP707106781 * (T52 - T53); T55 = T51 - T54; T5b = T51 + T54; } ro[(2 * 22)] = T4B - T4Y; io[(2 * 22)] = T5b - T5c; ro[(2 * 6)] = T4B + T4Y; io[(2 * 6)] = T5b + T5c; io[(2 * 30)] = T55 - T56; ro[(2 * 30)] = T57 - T5a; io[(2 * 14)] = T55 + T56; ro[(2 * 14)] = T57 + T5a; } { E T5f, T5r, T5u, T5w, T5m, T5q, T5p, T5v; { E T5d, T5e, T5s, T5t; T5d = T4r + T4s; T5e = KP707106781 * (T53 + T52); T5f = T5d + T5e; T5r = T5d - T5e; T5s = FNMS(KP382683432, T5h, KP923879532 * T5g); T5t = FMA(KP923879532, T5k, KP382683432 * T5j); T5u = T5s - T5t; T5w = T5s + T5t; } { E T5i, T5l, T5n, T5o; T5i = FMA(KP382683432, T5g, KP923879532 * T5h); T5l = FNMS(KP382683432, T5k, KP923879532 * T5j); T5m = T5i + T5l; T5q = T5l - T5i; T5n = T50 + T4Z; T5o = KP707106781 * (T4w + T4z); T5p = T5n - T5o; T5v = T5n + T5o; } ro[(2 * 18)] = T5f - T5m; io[(2 * 18)] = T5v - T5w; ro[(2 * 2)] = T5f + T5m; io[(2 * 2)] = T5v + T5w; io[(2 * 26)] = T5p - T5q; ro[(2 * 26)] = T5r - T5u; io[(2 * 10)] = T5p + T5q; ro[(2 * 10)] = T5r + T5u; } { E T5z, T5P, T5S, T5U, T5K, T5O, T5N, T5T; { E T5x, T5y, T5Q, T5R; T5x = T7 - Te; T5y = T1n - T1u; T5z = T5x + T5y; T5P = T5x - T5y; T5Q = T5D - T5A; T5R = T5F + T5I; T5S = KP707106781 * (T5Q - T5R); T5U = KP707106781 * (T5Q + T5R); } { E T5E, T5J, T5L, T5M; T5E = T5A + T5D; T5J = T5F - T5I; T5K = KP707106781 * (T5E + T5J); T5O = KP707106781 * (T5J - T5E); T5L = T18 - T1f; T5M = Tt - Tm; T5N = T5L - T5M; T5T = T5M + T5L; } ro[(2 * 20)] = T5z - T5K; io[(2 * 20)] = T5T - T5U; ro[(2 * 4)] = T5z + T5K; io[(2 * 4)] = T5T + T5U; io[(2 * 28)] = T5N - T5O; ro[(2 * 28)] = T5P - T5S; io[(2 * 12)] = T5N + T5O; ro[(2 * 12)] = T5P + T5S; } { E Tv, T5V, T5Y, T60, T10, T11, T1w, T5Z; { E Tf, Tu, T5W, T5X; Tf = T7 + Te; Tu = Tm + Tt; Tv = Tf + Tu; T5V = Tf - Tu; T5W = T5B + T5C; T5X = T5G + T5H; T5Y = T5W - T5X; T60 = T5W + T5X; } { E TK, TZ, T1g, T1v; TK = TC + TJ; TZ = TR + TY; T10 = TK + TZ; T11 = TZ - TK; T1g = T18 + T1f; T1v = T1n + T1u; T1w = T1g - T1v; T5Z = T1g + T1v; } ro[(2 * 16)] = Tv - T10; io[(2 * 16)] = T5Z - T60; ro[0] = Tv + T10; io[0] = T5Z + T60; io[(2 * 8)] = T11 + T1w; ro[(2 * 8)] = T5V + T5Y; io[(2 * 24)] = T1w - T11; ro[(2 * 24)] = T5V - T5Y; } { E T1X, T33, T31, T37, T2o, T34, T2P, T35; { E T1H, T1W, T2X, T30; T1H = T1z - T1G; T1W = T1O - T1V; T1X = T1H + T1W; T33 = T1H - T1W; T2X = T2T - T2W; T30 = T2Y - T2Z; T31 = T2X - T30; T37 = T2X + T30; } { E T2e, T2n, T2F, T2O; T2e = T22 - T2d; T2n = T2j - T2m; T2o = FMA(KP980785280, T2e, KP195090322 * T2n); T34 = FNMS(KP980785280, T2n, KP195090322 * T2e); T2F = T2t - T2E; T2O = T2K - T2N; T2P = FNMS(KP980785280, T2O, KP195090322 * T2F); T35 = FMA(KP195090322, T2O, KP980785280 * T2F); } { E T2Q, T38, T32, T36; T2Q = T2o + T2P; ro[(2 * 23)] = T1X - T2Q; ro[(2 * 7)] = T1X + T2Q; T38 = T34 + T35; io[(2 * 23)] = T37 - T38; io[(2 * 7)] = T37 + T38; T32 = T2P - T2o; io[(2 * 31)] = T31 - T32; io[(2 * 15)] = T31 + T32; T36 = T34 - T35; ro[(2 * 31)] = T33 - T36; ro[(2 * 15)] = T33 + T36; } } { E T3D, T41, T3Z, T45, T3K, T42, T3R, T43; { E T3v, T3C, T3V, T3Y; T3v = T3t - T3u; T3C = T3y - T3B; T3D = T3v + T3C; T41 = T3v - T3C; T3V = T3T - T3U; T3Y = T3W - T3X; T3Z = T3V - T3Y; T45 = T3V + T3Y; } { E T3G, T3J, T3N, T3Q; T3G = T3E - T3F; T3J = T3H - T3I; T3K = FMA(KP555570233, T3G, KP831469612 * T3J); T42 = FNMS(KP831469612, T3G, KP555570233 * T3J); T3N = T3L - T3M; T3Q = T3O - T3P; T3R = FNMS(KP831469612, T3Q, KP555570233 * T3N); T43 = FMA(KP831469612, T3N, KP555570233 * T3Q); } { E T3S, T46, T40, T44; T3S = T3K + T3R; ro[(2 * 21)] = T3D - T3S; ro[(2 * 5)] = T3D + T3S; T46 = T42 + T43; io[(2 * 21)] = T45 - T46; io[(2 * 5)] = T45 + T46; T40 = T3R - T3K; io[(2 * 29)] = T3Z - T40; io[(2 * 13)] = T3Z + T40; T44 = T42 - T43; ro[(2 * 29)] = T41 - T44; ro[(2 * 13)] = T41 + T44; } } { E T49, T4l, T4j, T4p, T4c, T4m, T4f, T4n; { E T47, T48, T4h, T4i; T47 = T3t + T3u; T48 = T3X + T3W; T49 = T47 + T48; T4l = T47 - T48; T4h = T3T + T3U; T4i = T3y + T3B; T4j = T4h - T4i; T4p = T4h + T4i; } { E T4a, T4b, T4d, T4e; T4a = T3E + T3F; T4b = T3H + T3I; T4c = FMA(KP980785280, T4a, KP195090322 * T4b); T4m = FNMS(KP195090322, T4a, KP980785280 * T4b); T4d = T3L + T3M; T4e = T3O + T3P; T4f = FNMS(KP195090322, T4e, KP980785280 * T4d); T4n = FMA(KP195090322, T4d, KP980785280 * T4e); } { E T4g, T4q, T4k, T4o; T4g = T4c + T4f; ro[(2 * 17)] = T49 - T4g; ro[(2 * 1)] = T49 + T4g; T4q = T4m + T4n; io[(2 * 17)] = T4p - T4q; io[(2 * 1)] = T4p + T4q; T4k = T4f - T4c; io[(2 * 25)] = T4j - T4k; io[(2 * 9)] = T4j + T4k; T4o = T4m - T4n; ro[(2 * 25)] = T4l - T4o; ro[(2 * 9)] = T4l + T4o; } } { E T3b, T3n, T3l, T3r, T3e, T3o, T3h, T3p; { E T39, T3a, T3j, T3k; T39 = T1z + T1G; T3a = T2Z + T2Y; T3b = T39 + T3a; T3n = T39 - T3a; T3j = T2T + T2W; T3k = T1O + T1V; T3l = T3j - T3k; T3r = T3j + T3k; } { E T3c, T3d, T3f, T3g; T3c = T22 + T2d; T3d = T2j + T2m; T3e = FMA(KP555570233, T3c, KP831469612 * T3d); T3o = FNMS(KP555570233, T3d, KP831469612 * T3c); T3f = T2t + T2E; T3g = T2K + T2N; T3h = FNMS(KP555570233, T3g, KP831469612 * T3f); T3p = FMA(KP831469612, T3g, KP555570233 * T3f); } { E T3i, T3s, T3m, T3q; T3i = T3e + T3h; ro[(2 * 19)] = T3b - T3i; ro[(2 * 3)] = T3b + T3i; T3s = T3o + T3p; io[(2 * 19)] = T3r - T3s; io[(2 * 3)] = T3r + T3s; T3m = T3h - T3e; io[(2 * 27)] = T3l - T3m; io[(2 * 11)] = T3l + T3m; T3q = T3o - T3p; ro[(2 * 27)] = T3n - T3q; ro[(2 * 11)] = T3n + T3q; } } } } /* END test.c */ >How-To-Repeat: See above. >Fix: Don't use -fnew-ra.