https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117184
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <[email protected]>: https://gcc.gnu.org/g:93352420faab917cc4b6fcf1127b9242fc9d25b0 commit r17-2511-g93352420faab917cc4b6fcf1127b9242fc9d25b0 Author: Matt Turner <[email protected]> Date: Sat Jul 18 10:32:39 2026 -0600 [PATCH] lra: mark the hard frame pointer live when LRA decides it is needed [PR117184] ira_setup_eliminable_regset calls df_set_regs_ever_live for the hard frame pointer when it decides frame_pointer_needed. LRA can reach that decision later instead, in setup_can_eliminate, when it finds the frame pointer to stack pointer elimination is not possible after all, but it does not mark the register live there. A target whose prologue decides which registers to save from df_regs_ever_live_p then sets up the frame pointer without saving the caller's value. On alpha this miscompiles pge while bootstrapping the Modula-2 front end (PR117184): alpha_compute_frame_layout leaves $15 out of the save mask, so alpha_expand_prologue emits the "mov $30,$15" that clobbers it but no matching store, while alpha_expand_epilogue restores the register whenever frame_pointer_needed, from an fp_offset that stayed 0 -- the return address slot. The caller gets its call-saved $15 back as a code address, which shows up much later as a NULL dereference, and the Modula-2 runtime turns the resulting SIGSEGV into an unhandled exception: terminate called after throwing an instance of 'unsigned int' The testcase needs the VLA to reach the caller by inlining: a caller with its own VLA has cfun->calls_alloca set, so IRA already knows a frame pointer is needed and marks $15 live itself. Do what IRA does, so the two paths agree. PR target/117184 gcc/ * lra-eliminations.cc (setup_can_eliminate): Mark the hard frame pointer live when setting frame_pointer_needed. gcc/testsuite/ * gcc.target/alpha/frame-pointer-save-1.c: New test.
