As is noted in the PR, the REG_CFA_DEF_DFA note is wrong for the testcase, while I get meaningfully different CFA note locations than the author, it is clear that the note is getting attached to the wrong insn.
The CFA_DEF_CFA note should get attached to the insn that copies from the stack pointer into the temporary. The RISC-V port tried to do that, but appears to have just gotten the logic wrong. The net is the CFA_DEF_CFA note got attached to the insn before the stack pointer copy. Worse yet the insn with the note could move around relative to the stack pointer for scheduling purposes.
The fix is trivial. We just need to attach the note to the sp->temp copy. Given this doesn't affect code generation, but is a correctness issue, I will go ahead and backport it immediately rather than waiting for the usual simmer on the trunk.
Bootstrapped and regression tested on the K3 and c920. Also tested for the riscv32-elf and riscv64-elf platforms.
Jeff
commit e3457d211e2720dd0f8070fe7600be4b026ed1ef Author: Jeff Law <[email protected]> Date: Sun Sep 13 08:49:47 2026 -0600 [RISC-V][PR target/127318] Attach DEF_CFA to correct insn As is noted in the PR, the REG_CFA_DEF_DFA note is wrong for the testcase, while I get meaningfully different CFA note locations than the author, it is clear that the note is getting attached to the wrong insn. The CFA_DEF_CFA note should get attached to the insn that copies from the stack pointer into the temporary. The RISC-V port tried to do that, but appears to have just gotten the logic wrong. The net is the CFA_DEF_CFA note got attached to the insn before the stack pointer copy. Worse yet the insn with the note could move around relative to the stack pointer for scheduling purposes. The fix is trivial. We just need to attach the note to the sp->temp copy. Given this doesn't affect code generation, but is a correctness issue, I will go ahead and backport it immediately rather than waiting for the usual simmer on the trunk. Bootstrapped and regression tested on the K3 and c920. Also tested for the riscv32-elf and riscv64-elf platforms. PR target/127318 gcc/ * config/riscv/riscv.cc (riscv_v_adjust_scalable_frame): Attach REG_CFA_DEF_CFA note to the copy from the stack pointer. diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc index 58c48bd1627..39309b2b205 100644 --- a/gcc/config/riscv/riscv.cc +++ b/gcc/config/riscv/riscv.cc @@ -10209,9 +10209,8 @@ riscv_v_adjust_scalable_frame (rtx target, poly_int64 offset, bool epilogue) very wrong) we tie the old and new stack pointer together. The tie will expand to nothing but the optimizers will not touch the instruction. */ - insn = get_last_insn (); rtx stack_ptr_copy = gen_rtx_REG (Pmode, RISCV_STACK_CLASH_VECTOR_CFA_REGNUM); - emit_move_insn (stack_ptr_copy, stack_pointer_rtx); + insn = emit_move_insn (stack_ptr_copy, stack_pointer_rtx); riscv_emit_stack_tie (stack_ptr_copy); /* We want the CFA independent of the stack pointer for the
