"H.J. Lu" <[email protected]> writes: > Since flow_active_insn_p has: > > if ((GET_CODE (PATTERN (insn)) == CLOBBER > || GET_CODE (PATTERN (insn)) == USE) > && REG_P (XEXP (PATTERN (insn), 0)) > && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0))) > return true; > > update DCE to always keep return value clobber. > > Adjust assembly scan in gcc.target/i386/zero-scratch-regs-30.c to also > expect 8 "fstp %st(0)" in 64-bit mode for extra insns: > > flds .LC2(%rip) // +QNaN > flds .LC2(%rip) // +QNaN > fstp %st(0) > fstp %st(0) > > since return value clobber: > > (insn 10 2 11 2 (clobber (reg/i:XC 8 st)) "zero-scratch-regs-30.c":7:1 -1 > (nil)) > > is no longer removed as without -fzero-call-used-regs=all. > > PR rtl-optimization/125375 > * dce.cc: (deletable_insn_p): Always keep return value clobber.
We shouldn't need to keep the clobber for correctness. It's just supposed to be an optimisation crutch to prevent the return register from becoming unnecessarily upwards exposed. I think there's a deeper issue here. Richard > > gcc/testsuite/ > > PR rtl-optimization/125375 > * gcc.target/i386/pr125375.c: New test. > * gcc.target/i386/zero-scratch-regs-30.c: Also expect 8 > "fstp %st(0)" in 64-bit mode. > > Signed-off-by: H.J. Lu <[email protected]> > Co-Developed-by: Andrew Pinski <[email protected]>
