On Tue, 2023-04-18 at 20:03 +0800, Lulu Cheng wrote: > > 在 2023/4/18 下午7:48, Xi Ruoyao 写道: > > On Tue, 2023-04-18 at 19:21 +0800, Lulu Cheng wrote: > > > 在 2023/4/18 下午5:27, Xi Ruoyao 写道: > > > > On Mon, 2023-04-10 at 17:45 +0800, Lulu Cheng wrote: > > > > > Sorry, it's my question. I still have some questions that I > > > > > haven't > > > > > understood, so I haven't replied to the email yet.:-( > > > > I've verified the value of cfun->va_list_gpr_size with -fdump- > > > > tree- > > > > stdarg and various testcases (including extracting aggregates > > > > and > > > > floating-point values in the va list) and the result seems > > > > correct. And > > > > gcc/testsuite/gcc.c-torture/execute/va-arg-*.c should provide a > > > > good > > > > enough test coverage. > > > > > > > > Is there still something seemly problematic? > > > > > > I think there is no problem with the code modification, but I > > > found that > > > the $r12 register is stored whether or not this patch is added. I > > > don't > > > understand why.:-( > > It has been stored before the change: > > > > test: > > .LFB0 = . > > .cfi_startproc > > addi.d $r3,$r3,-80 > > .cfi_def_cfa_offset 80 > > addi.d $r12,$r3,24 > > st.d $r5,$r3,24 > > st.d $r6,$r3,32 > > st.d $r7,$r3,40 > > st.d $r8,$r3,48 > > st.d $r9,$r3,56 > > st.d $r10,$r3,64 > > st.d $r11,$r3,72 > > st.d $r12,$r3,8 # <===== > > add.w $r4,$r5,$r4 > > addi.d $r3,$r3,80 > > .cfi_def_cfa_offset 0 > > jr $r1 > > .cfi_endproc > > > > AFAIK it's related to how the variable arguments are implemented in > > general. The problem is when we expands __builtin_va_list or > > __builtin_va_arg, the registers containing the variable arguments > > and > > the pointer to the variable argument store area (r12 in this case) > > may > > be already clobbered, so the compiler have to store them expanding > > the > > prologue of the function (when the prologue is expanded we don't > > know if > > the following code will clobber the registers). > > > > This also causes a difficulty to avoid saving the GARs for *used* > > variable arguments as well. > > > > On x86_64 we have the same issue: > > > > test: > > .LFB0: > > .cfi_startproc > > leaq 8(%rsp), %rax > > movq %rsi, -40(%rsp) > > movq %rax, -64(%rsp) # <===== > > leaq -48(%rsp), %rax > > movq %rax, -56(%rsp) > > movl -40(%rsp), %eax > > movl $8, -72(%rsp) > > addl %edi, %eax > > ret > > .cfi_endproc > > > > I'll try to remove all of these in the GCC 14 development cycle (as > > they > > are causing sub-optimal code in various Glibc functions), but it's > > not > > easy... > > > > > Ok, I have no more questions. > Pushed r14-69.
-- Xi Ruoyao <xry...@xry111.site> School of Aerospace Science and Technology, Xidian University
