From 54ef7701a9dec8c923a12d1983f8a051ba88a7b9 Mon Sep 17 00:00:00 2001 From: Richard Sandiford Date: Wed, 28 Oct 2020 19:05:49 +0000 Subject: [PATCH] value-range: Give up on POLY_INT_CST ranges [PR97457] This PR shows another problem with calculating value ranges for POLY_INT_CSTs. We have: ivtmp_76 = ASSERT_EXPR POLY_INT_CST [9, 4294967294]> where the VQ coefficient is unsigned but is effectively acting as a negative number. We wrongly give the POLY_INT_CST the range: [9, INT_MAX] and things go downhill from there: later iterations of the unrolled epilogue are wrongly removed as dead. I guess this is the final nail in the coffin for doing VRP on POLY_INT_CSTs. For other similarly exotic testcases we could have overflow for any coefficient, not just those that could be treated as contextually negative. Testing TYPE_OVERFLOW_UNDEFINED doesn't seem like an option because we couldn't handle warn_strict_overflow properly. At this stage we're just recording a range that might or might not lead to strict-overflow assumptions later. It still feels like we should be able to do something here, but for now removing the code seems safest. It's also telling that there are no testsuite failures on SVE from doing this. gcc/ PR tree-optimization/97457 * value-range.cc (irange::set): Don't decay POLY_INT_CST ranges to integer ranges. gcc/testsuite/ PR tree-optimization/97457 * gcc.dg/vect/pr97457.c: New test. --- gcc/testsuite/gcc.dg/vect/pr97457.c | 15 +++++++++++++++ gcc/value-range.cc | 30 +++++------------------------ 2 files changed, 20 insertions(+), 25 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/vect/pr97457.c diff --git a/gcc/testsuite/gcc.dg/vect/pr97457.c b/gcc/testsuite/gcc.dg/vect/pr97457.c new file mode 100644 index 00000000000..506ba249b00 --- /dev/null +++ b/gcc/testsuite/gcc.dg/vect/pr97457.c @@ -0,0 +1,15 @@ +/* { dg-additional-options "-O3" } */ + +int a; +long c; +signed char d(char e, char f) { return e + f; } +int main(void) { + for (; a <= 1; a++) { + c = -8; + for (; c != 3; c = d(c, 1)) + ; + } + char b = c; + if (b != 3) + __builtin_abort(); +} diff --git a/gcc/value-range.cc b/gcc/value-range.cc index 0e633c1c673..5827e812216 100644 --- a/gcc/value-range.cc +++ b/gcc/value-range.cc @@ -248,31 +248,11 @@ irange::set (tree min, tree max, value_range_kind kind) set_undefined (); return; } - if (kind == VR_RANGE) - { - /* Convert POLY_INT_CST bounds into worst-case INTEGER_CST bounds. */ - if (POLY_INT_CST_P (min)) - { - tree type_min = vrp_val_min (TREE_TYPE (min)); - widest_int lb - = constant_lower_bound_with_limit (wi::to_poly_widest (min), - wi::to_widest (type_min)); - min = wide_int_to_tree (TREE_TYPE (min), lb); - } - if (POLY_INT_CST_P (max)) - { - tree type_max = vrp_val_max (TREE_TYPE (max)); - widest_int ub - = constant_upper_bound_with_limit (wi::to_poly_widest (max), - wi::to_widest (type_max)); - max = wide_int_to_tree (TREE_TYPE (max), ub); - } - } - else if (kind != VR_VARYING) - { - if (POLY_INT_CST_P (min) || POLY_INT_CST_P (max)) - kind = VR_VARYING; - } + + if (kind != VR_VARYING + && (POLY_INT_CST_P (min) || POLY_INT_CST_P (max))) + kind = VR_VARYING; + if (kind == VR_VARYING) { set_varying (TREE_TYPE (min)); -- 2.30.2