| Message ID | 87d2y0vhms.fsf@talisman.default |
|---|---|
| State | New |
| Headers | show |
On Sun, Dec 23, 2012 at 5:48 PM, Richard Sandiford <rdsandiford@googlemail.com> wrote: > The minimum uint128_t value is an all-zeros double_int and the maximum > value is an all-ones double_int. Truncating these values to int and > then sign-extending them gives the same all-zeros and all-ones values, > so tree-vrp.c:range_fits_type_p concludes that uint128_t fits in an int. > > This showed up as a miscompilation of __fractutasf on mips64-linux-gnu, > which in turn showed up in convert-float-4.c. > > There was already code to handle this problem when changing the sign > and keeping the precision, but I think the rule applies regardless > of precision. > > Tested on x86_64-linux-gnu and mips64-linux-gnu. OK to install? Ok. Thanks, Richard. > Richard > > > gcc/ > * tree-vrp.c (range_fits_type_p): Require the MSB of the double_int > to be clear for sign changes. > > gcc/testsuite/ > * gcc.dg/torture/fp-int-convert-2.c: New test. > > Index: gcc/tree-vrp.c > =================================================================== > --- gcc/tree-vrp.c 2012-12-23 11:50:39.046419271 +0000 > +++ gcc/tree-vrp.c 2012-12-23 11:51:17.814677008 +0000 > @@ -8766,9 +8766,11 @@ range_fits_type_p (value_range_t *vr, un > || TREE_CODE (vr->max) != INTEGER_CST) > return false; > > - /* For precision-preserving sign-changes the MSB of the double-int > - has to be clear. */ > - if (src_precision == precision > + /* For sign changes, the MSB of the double_int has to be clear. > + An unsigned value with its MSB set cannot be represented by > + a signed double_int, while a negative value cannot be represented > + by an unsigned double_int. */ > + if (TYPE_UNSIGNED (src_type) != unsigned_p > && (TREE_INT_CST_HIGH (vr->min) | TREE_INT_CST_HIGH (vr->max)) < 0) > return false; > > Index: gcc/testsuite/gcc.dg/torture/fp-int-convert-2.c > =================================================================== > --- /dev/null 2012-12-03 19:06:31.446621561 +0000 > +++ gcc/testsuite/gcc.dg/torture/fp-int-convert-2.c 2012-12-23 13:46:35.449077882 +0000 > @@ -0,0 +1,18 @@ > +/* { dg-do run } */ > +/* { dg-require-effective-target int128 } */ > + > +extern void abort (void); > + > +float __attribute__((noinline)) > +f (__uint128_t x) > +{ > + return x + 1; > +} > + > +int > +main (void) > +{ > + if (f (0xffffffffu) == 0) > + abort (); > + return 0; > +}
Index: gcc/tree-vrp.c =================================================================== --- gcc/tree-vrp.c 2012-12-23 11:50:39.046419271 +0000 +++ gcc/tree-vrp.c 2012-12-23 11:51:17.814677008 +0000 @@ -8766,9 +8766,11 @@ range_fits_type_p (value_range_t *vr, un || TREE_CODE (vr->max) != INTEGER_CST) return false; - /* For precision-preserving sign-changes the MSB of the double-int - has to be clear. */ - if (src_precision == precision + /* For sign changes, the MSB of the double_int has to be clear. + An unsigned value with its MSB set cannot be represented by + a signed double_int, while a negative value cannot be represented + by an unsigned double_int. */ + if (TYPE_UNSIGNED (src_type) != unsigned_p && (TREE_INT_CST_HIGH (vr->min) | TREE_INT_CST_HIGH (vr->max)) < 0) return false; Index: gcc/testsuite/gcc.dg/torture/fp-int-convert-2.c =================================================================== --- /dev/null 2012-12-03 19:06:31.446621561 +0000 +++ gcc/testsuite/gcc.dg/torture/fp-int-convert-2.c 2012-12-23 13:46:35.449077882 +0000 @@ -0,0 +1,18 @@ +/* { dg-do run } */ +/* { dg-require-effective-target int128 } */ + +extern void abort (void); + +float __attribute__((noinline)) +f (__uint128_t x) +{ + return x + 1; +} + +int +main (void) +{ + if (f (0xffffffffu) == 0) + abort (); + return 0; +}