https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120721
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Richard Sandiford <[email protected]>: https://gcc.gnu.org/g:8130a2ad91ca8571b099ba020443fadab7a688ca commit r16-1621-g8130a2ad91ca8571b099ba020443fadab7a688ca Author: Richard Sandiford <[email protected]> Date: Mon Jun 23 08:46:27 2025 +0100 vregs: Use force_subreg when instantiating subregs [PR120721] In this PR, we started with: (subreg:V2DI (reg:DI virtual-reg) 0) and vregs instantiated the virtual register to the argument pointer. But: (subreg:V2DI (reg:DI ap) 0) is not a sensible subreg, since the argument pointer certainly can't be referenced in V2DImode. This is (IMO correctly) rejected after g:2dcc6dbd8a00caf7cfa8cac17b3fd1c33d658016. The vregs code that instantiates the subreg above is specific to rvalues and already creates new instructions for nonzero offsets. It is therefore safe to use force_subreg instead of simplify_gen_subreg. I did wonder whether we should instead say that a subreg of a virtual register is invalid if the same subreg would be invalid for the associated hard registers. But the point of virtual registers is that the offsets from the hard registers are not known until after expand has finished, and if an offset is nonzero, the virtual register will be instantiated into a pseudo that contains the sum of the hard register and the offset. The subreg would then be correct for that pseudo. The subreg is only invalid in this case because there is no offset. gcc/ PR rtl-optimization/120721 * function.cc (instantiate_virtual_regs_in_insn): Use force_subreg instead of simplify_gen_subreg when instantiating an rvalue SUBREG. gcc/testsuite/ PR rtl-optimization/120721 * g++.dg/torture/pr120721.C: New test.
