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. Uros.
