On Tue, May 12, 2026 at 8:47 AM H.J. Lu <[email protected]> wrote: > > On Tue, May 12, 2026 at 2:39 PM Uros Bizjak <[email protected]> wrote: > > > > On Tue, May 12, 2026 at 2:42 AM H.J. Lu <[email protected]> wrote: > > > > > > DRAP register is used to restore stack pointer in epilogue for stack > > > realignment. In no-callee-saved and preserve_none functions, although > > > DRAP register isn't preserved, it must be unchanged between prologue > > > and epilogue so that stack pointer can be restored. In no-callee-saved > > > and preserve_none functions, mark BX_REG as fixed and use it for DRAP > > > register. > > > > > > NB: r12-r15 aren't made available as the local general purpose registers > > > since it causes: > > > > > > FAIL: gcc.target/i386/preserve-none-1.c scan-assembler-not movq > > > FAIL: gcc.target/i386/preserve-none-30a.c check-function-bodies entry > > > FAIL: gcc.target/i386/preserve-none-30b.c check-function-bodies entry > > > > > > which have the same cause as > > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124798 > > > > > > gcc/ > > > > > > PR target/120870 > > > * config/i386/i386.cc (X86_NO_CALLEE_DRAP_REG): New. > > > (ix86_conditional_register_usage): Mark X86_NO_CALLEE_DRAP_REG > > > as fixed. > > > (find_drap_reg): Return X86_PRESERVE_NONE_DRAP_REG for > > > no-callee-saved and preserve_none functions > > > > > > gcc/testsuite/ > > > > > > PR target/120870 > > > * gcc.target/i386/pr120870-1.c: New test. > > > * gcc.target/i386/pr120870-2.c: Likewise. > > > > + case TYPE_NO_CALLEE_SAVED_REGISTERS: > > + case TYPE_PRESERVE_NONE: > > + /* DRAP register is used to restore stack pointer in epilogue > > + for stack realignment. Although DRAP register isn't > > + preserved, it must be unchanged between prologue and > > + epilogue so that stack pointer can be restored. In > > + no-callee-saved and preserve_none function, mark BX_REG > > + as fixed and use it for DRAP register. */ > > + fixed_regs[X86_NO_CALLEE_DRAP_REG] = 1; > > > > Isn't this hammer too big? This will remove RBX even when DRAP is not > > needed, which I assume is in the majority of cases. > > > > It is only for preserve_none functions where all, but BX, SP, FP, are > scratch registers. It should be OK.
But your patch returns X86_NO_CALLEE_DRAP_REG (AKA RBX) from find_drap_reg. This should signal RA that the register is unavailable. Why doesn't it? Uros.
