On Wed, 2022-03-09 at 15:55 +0100, Richard Biener wrote: > isn't it better to make targetm.const_anchor unsigned? > The & and ~ are not subject to overflow rules.
It's not enough: if n is the minimum value of HOST_WIDE_INT and const_anchor = 0x8000 (the value for MIPS), we'll have a signed 0x7fff in *upper_base. Then the next line, "*upper_offs = n - *upper_base;" will be a signed overflow again. How about the following? -- >8 -- With a non-zero const_anchor, the behavior of this function relied on signed overflow. gcc/ PR rtl-optimization/104843 * cse.cc (compute_const_anchors): Use unsigned HOST_WIDE_INT for n to perform overflow arithmetics safely. --- gcc/cse.cc | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/gcc/cse.cc b/gcc/cse.cc index a18b599d324..052fa0c3490 100644 --- a/gcc/cse.cc +++ b/gcc/cse.cc @@ -1169,12 +1169,12 @@ compute_const_anchors (rtx cst, HOST_WIDE_INT *lower_base, HOST_WIDE_INT *lower_offs, HOST_WIDE_INT *upper_base, HOST_WIDE_INT *upper_offs) { - HOST_WIDE_INT n = INTVAL (cst); - - *lower_base = n & ~(targetm.const_anchor - 1); - if (*lower_base == n) + unsigned HOST_WIDE_INT n = UINTVAL (cst); + unsigned HOST_WIDE_INT lb = n & ~(targetm.const_anchor - 1); + if (lb == n) return false; + *lower_base = lb; *upper_base = (n + (targetm.const_anchor - 1)) & ~(targetm.const_anchor - 1); *upper_offs = n - *upper_base; -- 2.35.1 >