On Wed, Nov 20, 2013 at 7:17 PM, Joseph S. Myers <jos...@codesourcery.com> wrote: > On Wed, 20 Nov 2013, Richard Biener wrote: > >> I suggest to remove real_sqrt and the only use in simplify-rtx.c instead >> (or fix it to use MPFR as well - your choice). > > This patch removes real_sqrt. (I rather hope that in general little > if any floating-point constant folding is happening on RTL - it > doesn't seem like the sort of thing for which RTL expansion should be > expected to introduce new folding opportunities, and if it does I'd > tend to think that indicates a deficiency in the GIMPLE optimizers.) > > Bootstrapped with no regressions on x86_64-unknown-linux-gnu. OK to > commit?
Ok. Thanks, Richard. > 2013-11-20 Joseph Myers <jos...@codesourcery.com> > > * real.c (real_sqrt): Remove function. > * real.h (real_sqrt): Remove prototype. > * simplify-rtx.c (simplify_const_unary_operation): Do not fold > SQRT using real_sqrt. > > Index: gcc/real.c > =================================================================== > --- gcc/real.c (revision 205119) > +++ gcc/real.c (working copy) > @@ -4765,84 +4765,6 @@ const struct real_format real_internal_format = > false > }; > > -/* Calculate the square root of X in mode MODE, and store the result > - in R. Return TRUE if the operation does not raise an exception. > - For details see "High Precision Division and Square Root", > - Alan H. Karp and Peter Markstein, HP Lab Report 93-93-42, June > - 1993. http://www.hpl.hp.com/techreports/93/HPL-93-42.pdf. */ > - > -bool > -real_sqrt (REAL_VALUE_TYPE *r, enum machine_mode mode, > - const REAL_VALUE_TYPE *x) > -{ > - static REAL_VALUE_TYPE halfthree; > - static bool init = false; > - REAL_VALUE_TYPE h, t, i; > - int iter, exp; > - > - /* sqrt(-0.0) is -0.0. */ > - if (real_isnegzero (x)) > - { > - *r = *x; > - return false; > - } > - > - /* Negative arguments return NaN. */ > - if (real_isneg (x)) > - { > - get_canonical_qnan (r, 0); > - return false; > - } > - > - /* Infinity and NaN return themselves. */ > - if (!real_isfinite (x)) > - { > - *r = *x; > - return false; > - } > - > - if (!init) > - { > - do_add (&halfthree, &dconst1, &dconsthalf, 0); > - init = true; > - } > - > - /* Initial guess for reciprocal sqrt, i. */ > - exp = real_exponent (x); > - real_ldexp (&i, &dconst1, -exp/2); > - > - /* Newton's iteration for reciprocal sqrt, i. */ > - for (iter = 0; iter < 16; iter++) > - { > - /* i(n+1) = i(n) * (1.5 - 0.5*i(n)*i(n)*x). */ > - do_multiply (&t, x, &i); > - do_multiply (&h, &t, &i); > - do_multiply (&t, &h, &dconsthalf); > - do_add (&h, &halfthree, &t, 1); > - do_multiply (&t, &i, &h); > - > - /* Check for early convergence. */ > - if (iter >= 6 && real_identical (&i, &t)) > - break; > - > - /* ??? Unroll loop to avoid copying. */ > - i = t; > - } > - > - /* Final iteration: r = i*x + 0.5*i*x*(1.0 - i*(i*x)). */ > - do_multiply (&t, x, &i); > - do_multiply (&h, &t, &i); > - do_add (&i, &dconst1, &h, 1); > - do_multiply (&h, &t, &i); > - do_multiply (&i, &dconsthalf, &h); > - do_add (&h, &t, &i, 0); > - > - /* ??? We need a Tuckerman test to get the last bit. */ > - > - real_convert (r, mode, &h); > - return true; > -} > - > /* Calculate X raised to the integer exponent N in mode MODE and store > the result in R. Return true if the result may be inexact due to > loss of precision. The algorithm is the classic "left-to-right binary > Index: gcc/real.h > =================================================================== > --- gcc/real.h (revision 205119) > +++ gcc/real.h (working copy) > @@ -461,10 +461,6 @@ bool real_can_shorten_arithmetic (enum machine_mod > /* In tree.c: wrap up a REAL_VALUE_TYPE in a tree node. */ > extern tree build_real (tree, REAL_VALUE_TYPE); > > -/* Calculate R as the square root of X in the given machine mode. */ > -extern bool real_sqrt (REAL_VALUE_TYPE *, enum machine_mode, > - const REAL_VALUE_TYPE *); > - > /* Calculate R as X raised to the integer exponent N in mode MODE. */ > extern bool real_powi (REAL_VALUE_TYPE *, enum machine_mode, > const REAL_VALUE_TYPE *, HOST_WIDE_INT); > Index: gcc/simplify-rtx.c > =================================================================== > --- gcc/simplify-rtx.c (revision 205119) > +++ gcc/simplify-rtx.c (working copy) > @@ -1931,17 +1931,13 @@ simplify_const_unary_operation (enum rtx_code code > && SCALAR_FLOAT_MODE_P (mode) > && SCALAR_FLOAT_MODE_P (GET_MODE (op))) > { > - REAL_VALUE_TYPE d, t; > + REAL_VALUE_TYPE d; > REAL_VALUE_FROM_CONST_DOUBLE (d, op); > > switch (code) > { > case SQRT: > - if (HONOR_SNANS (mode) && real_isnan (&d)) > - return 0; > - real_sqrt (&t, mode, &d); > - d = t; > - break; > + return 0; > case ABS: > d = real_value_abs (&d); > break; > > -- > Joseph S. Myers > jos...@codesourcery.com
