On Mon, 11 Oct 2021, Tamar Christina wrote: > Hi all, > > Here's a new version of the patch. > > > >>> " If an exceptional condition occurs during the evaluation of an > > >>> expression > > >> (that is, if the result is not mathematically defined or not in the > > >> range of representable values for its type), the behavior is undefined." > > >>> > > >>> So it should still be acceptable to do in this case. > > >> > > >> -fwrapv > > > > > > If I understand correctly, you're happy with this is I guard it on ! > > > flag_wrapv ? > > > > I did some more digging. Right shift of a negative value is IMP_DEF (not > > UNDEF - this keeps catching me out). So yes, wrapping this with !wrapv > > would address my concern. > > > > I've not reviewed the patch itself, though. I've never even written a patch > > for match.pd, so don't feel qualified to do that. > > No problem, thanks for catching this! I'm sure one of the Richards will > review it when > they have a chance. > > Bootstrapped Regtested on aarch64-none-linux-gnu, > x86_64-pc-linux-gnu and no regressions. > > Ok for master? > > Thanks, > Tamar > > gcc/ChangeLog: > > * match.pd: New negate+shift pattern. > > gcc/testsuite/ChangeLog: > > * gcc.dg/signbit-2.c: New test. > * gcc.dg/signbit-3.c: New test. > * gcc.target/aarch64/signbit-1.c: New test. > > --- inline copy of patch --- > > diff --git a/gcc/match.pd b/gcc/match.pd > index > 7d2a24dbc5e9644a09968f877e12a824d8ba1caa..3d48eda826f889483a83267409c3f278ee907b57 > 100644 > --- a/gcc/match.pd > +++ b/gcc/match.pd > @@ -826,6 +826,38 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > { tree utype = unsigned_type_for (type); } > (convert (rshift (lshift (convert:utype @0) @2) @3)))))) > > +/* Fold (-x >> C) into x > 0 where C = precision(type) - 1. */ > +(for cst (INTEGER_CST VECTOR_CST) > + (simplify > + (rshift (negate:s @0) cst@1) > + (if (!flag_wrapv)
Don't test flag_wrapv directly, instead use the appropriate TYPE_OVERFLOW_{UNDEFINED,WRAPS} predicates. But I'm not sure what we are protecting against? Right-shift of signed integers is implementation-defined and GCC treats it as you'd expect, sign-extending the result. > + (with { tree ctype = TREE_TYPE (@0); > + tree stype = TREE_TYPE (@1); > + tree bt = truth_type_for (ctype); } > + (switch > + /* Handle scalar case. */ > + (if (INTEGRAL_TYPE_P (ctype) > + && !VECTOR_TYPE_P (ctype) > + && !TYPE_UNSIGNED (ctype) > + && canonicalize_math_after_vectorization_p () > + && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1)) > + (convert:bt (gt:bt @0 { build_zero_cst (stype); }))) I'm not sure why the result is of type 'bt' rather than the original type of the expression? In that regard for non-vectors we'd have to add the sign extension from unsigned bool, in the vector case we'd hope the type of the comparison is correct. I think in both cases it might be convenient to use (cond (gt:bt @0 { build_zero_cst (ctype); }) { build_all_ones_cst (ctype); } { build_zero_cost (ctype); }) to compute the correct result and rely on (cond ..) simplifications to simplify that if possible. Btw, 'stype' should be irrelevant - you need to look at the precision of 'ctype', no? Richard. > + /* Handle vector case with a scalar immediate. */ > + (if (VECTOR_INTEGER_TYPE_P (ctype) > + && !VECTOR_TYPE_P (stype) > + && !TYPE_UNSIGNED (ctype) > + && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1)) > + (convert:bt (gt:bt @0 { build_zero_cst (ctype); }))) > + /* Handle vector case with a vector immediate. */ > + (if (VECTOR_INTEGER_TYPE_P (ctype) > + && VECTOR_TYPE_P (stype) > + && !TYPE_UNSIGNED (ctype) > + && uniform_vector_p (@1)) > + (with { tree cst = vector_cst_elt (@1, 0); > + tree t = TREE_TYPE (cst); } > + (if (wi::eq_p (wi::to_wide (cst), TYPE_PRECISION (t) - 1)) > + (convert:bt (gt:bt @0 { build_zero_cst (ctype); })))))))))) > + > /* Fold (C1/X)*C2 into (C1*C2)/X. */ > (simplify > (mult (rdiv@3 REAL_CST@0 @1) REAL_CST@2) > diff --git a/gcc/testsuite/gcc.dg/signbit-2.c > b/gcc/testsuite/gcc.dg/signbit-2.c > new file mode 100644 > index > 0000000000000000000000000000000000000000..fc0157cbc5c7996b481f2998bc30176c96a669bb > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/signbit-2.c > @@ -0,0 +1,19 @@ > +/* { dg-do assemble } */ > +/* { dg-options "-O3 --save-temps -fdump-tree-optimized" } */ > + > +#include <stdint.h> > + > +void fun1(int32_t *x, int n) > +{ > + for (int i = 0; i < (n & -16); i++) > + x[i] = (-x[i]) >> 31; > +} > + > +void fun2(int32_t *x, int n) > +{ > + for (int i = 0; i < (n & -16); i++) > + x[i] = (-x[i]) >> 30; > +} > + > +/* { dg-final { scan-tree-dump-times {\s+>\s+\{ 0, 0, 0, 0 \}} 1 optimized } > } */ > +/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */ > diff --git a/gcc/testsuite/gcc.dg/signbit-3.c > b/gcc/testsuite/gcc.dg/signbit-3.c > new file mode 100644 > index > 0000000000000000000000000000000000000000..19e9c06c349b3287610f817628f00938ece60bf7 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/signbit-3.c > @@ -0,0 +1,13 @@ > +/* { dg-do assemble } */ > +/* { dg-options "-O1 --save-temps -fdump-tree-optimized" } */ > + > +#include <stdint.h> > + > +void fun1(int32_t *x, int n) > +{ > + for (int i = 0; i < (n & -16); i++) > + x[i] = (-x[i]) >> 31; > +} > + > +/* { dg-final { scan-tree-dump-times {\s+>\s+0;} 1 optimized } } */ > +/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */ > diff --git a/gcc/testsuite/gcc.target/aarch64/signbit-1.c > b/gcc/testsuite/gcc.target/aarch64/signbit-1.c > new file mode 100644 > index > 0000000000000000000000000000000000000000..3ebfb0586f37de29cf58635b27fe48503714447e > --- /dev/null > +++ b/gcc/testsuite/gcc.target/aarch64/signbit-1.c > @@ -0,0 +1,18 @@ > +/* { dg-do assemble } */ > +/* { dg-options "-O3 --save-temps" } */ > + > +#include <stdint.h> > + > +void fun1(int32_t *x, int n) > +{ > + for (int i = 0; i < (n & -16); i++) > + x[i] = (-x[i]) >> 31; > +} > + > +void fun2(int32_t *x, int n) > +{ > + for (int i = 0; i < (n & -16); i++) > + x[i] = (-x[i]) >> 30; > +} > + > +/* { dg-final { scan-assembler-times {\tcmgt\t} 1 } } */ > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)