On 01/02/2018 02:57 AM, Jakub Jelinek wrote: > On Mon, Jan 01, 2018 at 03:31:46PM -0700, Martin Sebor wrote: >> The ICE in the test case submitted in PR tree-optimization/83640 >> is triggered by the tree-ssa-strlen pass transforming calls to >> strcat to strcpy with an offset pointing to the terminating NUL >> of the destination string, and allowing the upper bound of the >> offset's range to exceed PTRDIFF_MAX by the length of >> the appended constant string. Although the ICE itself is due >> to an unsafe assumption in the -Wrestrict checker, the excessive >> upper bound in the strcat case suggests an optimization opportunity >> that's missing from the tree-ssa-strlen pass: namely, to reduce >> the offset's upper bound by the length of the appended string. >> The attached patch adds this minor optimization. > > This is wrong for many reasons. > > The recorded range info is a property of the SSA_NAME, can't be dependent on > where it is used, you are changing it globally. Right. And that's precisely the way to think about it -- does the range hold everywhere the SSA_NAME is or might be used. If so, then the range can be recorded via set_range_info.
Otherwise the range is context sensitive. The best way to handle context sensitive ranges is discover them within the EVRP analyzer which has mechanisms to record temporary ranges and reset them to their prior values when leaving scope. tree-ssa-strlen is already a dominator walker, so embedding an EVRP range analyzer in there ought to be trivial. Jeff
