https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71321
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:71197a5d13d0b540a9b5efe7ae2512d76386e9d1 commit r11-2621-g71197a5d13d0b540a9b5efe7ae2512d76386e9d1 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Sun Aug 9 23:14:58 2020 +0100 middle-end: Correct calculation of mul_widen_cost and mul_highpart_cost. This patch fixes a subtle bug in the depths of GCC's synth_mult, where the middle-end queries whether (how well) the target supports widening and highpart multiplications by calling targetm.rtx_costs. The code in init_expmed and init_expmed_one_mode iterates over various RTL patterns querying the cost of each. To avoid generating & garbage collecting too much junk, it reuses the same RTL over and over, but adjusting the modes between each call. Alas this reuse of state is a little fragile, and at some point a change to init_expmed_one_conv has resulted in the state (mode of a register) being changed, but not reset before being used again. Using the old software engineering/defensive programming maxim of "why fix a bug just once, if it can be fixed in multiple places", this patch both restores the original value in init_expmed_one_conv, and also sets it to the expected value in init_expmed_one_mode. This should hopefully signal the need to be careful of invariants for anyone modifying this code in future. 2020-08-09 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * expmed.c (init_expmed_one_conv): Restore all->reg's mode. (init_expmed_one_mode): Set all->reg to desired mode. gcc/testsuite/ChangeLog PR target/71321 * gcc.target/i386/pr71321.c: Check that the code doesn't use the 4B zero displacement lea, not that it uses lea.
