On February 19, 2018 11:02:50 PM GMT+01:00, Jakub Jelinek <ja...@redhat.com>
wrote:
>Hi!
>
>While I've over-simplified the testcase and so this patch doesn't help
>the 628.pop2_s miscompare, I still believe it is beneficial to defer
>this
>folding until late for these reasons:
>1) if we propagate a constant into the second pow argument too, it will
> be likely more precise than going through the exp (cst * x) way
>2) except when C is M_E, pow is fewer operations and thus smaller IL
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
>2018-02-19 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/82004
> * match.pd (pow(C,x) -> exp(log(C)*x)): Delay all folding until
> after vectorization.
>
> * gfortran.dg/pr82004.f90: New test.
>
>--- gcc/match.pd.jj 2018-02-15 12:15:51.655780636 +0100
>+++ gcc/match.pd 2018-02-19 17:38:06.390763194 +0100
>@@ -4006,7 +4006,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (simplify
> (pows REAL_CST@0 @1)
> (if (real_compare (GT_EXPR, TREE_REAL_CST_PTR (@0), &dconst0)
>- && real_isfinite (TREE_REAL_CST_PTR (@0)))
>+ && real_isfinite (TREE_REAL_CST_PTR (@0))
>+ /* As libmvec doesn't have a vectorized exp2, defer optimizing
>+ the use_exp2 case until after vectorization. It seems actually
>+ beneficial for all constants to postpone this until later,
>+ because exp(log(C)*x), while faster, will have worse precision
>+ and if x folds into a constant too, that is unnecessary
>+ pessimization. */
>+ && canonicalize_math_after_vectorization_p ())
> (with {
> const REAL_VALUE_TYPE *const value = TREE_REAL_CST_PTR (@0);
> bool use_exp2 = false;
>@@ -4021,10 +4028,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> }
> (if (!use_exp2)
> (exps (mult (logs @0) @1))
>- /* As libmvec doesn't have a vectorized exp2, defer optimizing
>- this until after vectorization. */
>- (if (canonicalize_math_after_vectorization_p ())
>- (exp2s (mult (log2s @0) @1))))))))
>+ (exp2s (mult (log2s @0) @1)))))))
>
> (for sqrts (SQRT)
> cbrts (CBRT)
>--- gcc/testsuite/gfortran.dg/pr82004.f90.jj 2018-02-19
>17:58:57.435682156 +0100
>+++ gcc/testsuite/gfortran.dg/pr82004.f90 2018-02-19 17:58:34.127684892
>+0100
>@@ -0,0 +1,18 @@
>+! PR middle-end/82004
>+! { dg-do run }
>+! { dg-options "-Ofast" }
>+
>+ integer, parameter :: r8 = selected_real_kind(13), i4 = kind(1)
>+ integer (i4), parameter :: a = 400, b = 2
>+ real (r8), parameter, dimension(b) :: c = (/ .001_r8, 10.00_r8 /)
>+ real (r8) :: d, e, f, g, h
>+ real (r8), parameter :: j &
>+ = 10**(log10(c(1))-(log10(c(b))-log10(c(1)))/real(a))
>+
>+ d = c(1)
>+ e = c(b)
>+ f = (log10(e)-log10(d))/real(a)
>+ g = log10(d) - f
>+ h = 10**(g)
>+ if (h.ne.j) stop 1
>+end
>
> Jakub
