https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109800
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-12 branch has been updated by Alex Coplan <acop...@gcc.gnu.org>: https://gcc.gnu.org/g:43619dc6e120a80305d4a52d7f9b8833c110a7db commit r12-9684-g43619dc6e120a80305d4a52d7f9b8833c110a7db Author: Alex Coplan <alex.cop...@arm.com> Date: Thu May 25 13:34:46 2023 +0100 arm: Fix ICE due to infinite splitting [PR109800] In r11-966-g9a182ef9ee011935d827ab5c6c9a7cd8e22257d8 we introduce a simplification to emit_move_insn that attempts to simplify moves of the form: (set (subreg:M1 (reg:M2 ...)) (constant C)) where M1 and M2 are of equal mode size. That is problematic for the splitter vfp.md:no_literal_pool_df_immediate in the arm backend, which tries to pun an lvalue DFmode pseudo into DImode and assign a constant to it with emit_move_insn, as the new transformation simply undoes this, and we end up splitting indefinitely. This patch changes things around in the arm backend so that we use a DImode temporary (instead of DFmode) and first load the DImode constant into the pseudo, and then pun the pseudo into DFmode as an rvalue in a reg -> reg move. I believe this should be semantically equivalent but avoids the pathalogical behaviour seen in the PR. gcc/ChangeLog: PR target/109800 * config/arm/arm.md (movdf): Generate temporary pseudo in DImode instead of DFmode. * config/arm/vfp.md (no_literal_pool_df_immediate): Rather than punning an lvalue DFmode pseudo into DImode, use a DImode pseudo and pun it into DFmode as an rvalue. gcc/testsuite/ChangeLog: PR target/109800 * gcc.target/arm/pure-code/pr109800.c: New test. (cherry picked from commit f5298d9969b4fa34ff3aecd54b9630e22b2984a5)
