[gcc r12-8558] LoongArch: Modify fp_sp_offset and gp_sp_offset's calculation method when frame->mask or frame->fmas

[LuluCheng <chenglulu@gcc.gnu.org>]

https://gcc.gnu.org/g:e623829c18ec2949f8b43a5a13775659e0cd1cbf

commit r12-8558-ge623829c18ec2949f8b43a5a13775659e0cd1cbf
Author: Lulu Cheng <chenglulu@loongson.cn>
Date:   Thu Jul 7 18:07:28 2022 +0800

    LoongArch: Modify fp_sp_offset and gp_sp_offset's calculation method when frame->mask or frame->fmask is zero.
    
    Under the LA architecture, when the stack is dropped too far, the process
    of dropping the stack is divided into two steps.
    step1: After dropping the stack, save callee saved registers on the stack.
    step2: The rest of it.
    
    The stack drop operation is optimized when frame->total_size minus
    frame->sp_fp_offset is an integer multiple of 4096, can reduce the number
    of instructions required to drop the stack. However, this optimization is
    not effective because of the original calculation method
    
    The following case:
            int main()
            {
              char buf[1024 * 12];
              printf ("%p\n", buf);
              return 0;
            }
    
    As you can see from the generated assembler, the old GCC has two more
    instructions than the new GCC, lines 14 and line 24.
    
               new                                        old
     10 main:                       | 11 main:
     11   addi.d  $r3,$r3,-16       | 12   lu12i.w $r13,-12288>>12
     12   lu12i.w $r13,-12288>>12   | 13   addi.d  $r3,$r3,-2032
     13   lu12i.w $r5,-12288>>12    | 14   ori $r13,$r13,2016
     14   lu12i.w $r12,12288>>12    | 15   lu12i.w $r5,-12288>>12
     15   st.d  $r1,$r3,8           | 16   lu12i.w $r12,12288>>12
     16   add.d $r12,$r12,$r5       | 17   st.d  $r1,$r3,2024
     17   add.d $r3,$r3,$r13        | 18   add.d $r12,$r12,$r5
     18   add.d $r5,$r12,$r3        | 19   add.d $r3,$r3,$r13
     19   la.local  $r4,.LC0        | 20   add.d $r5,$r12,$r3
     20   bl  %plt(printf)          | 21   la.local  $r4,.LC0
     21   lu12i.w $r13,12288>>12    | 22   bl  %plt(printf)
     22   add.d $r3,$r3,$r13        | 23   lu12i.w $r13,8192>>12
     23   ld.d  $r1,$r3,8           | 24   ori $r13,$r13,2080
     24   or  $r4,$r0,$r0           | 25   add.d $r3,$r3,$r13
     25   addi.d  $r3,$r3,16        | 26   ld.d  $r1,$r3,2024
     26   jr  $r1                   | 27   or  $r4,$r0,$r0
                                    | 28   addi.d  $r3,$r3,2032
                                    | 29   jr  $r1
    gcc/ChangeLog:
    
            * config/loongarch/loongarch.cc (loongarch_compute_frame_info):
            Modify fp_sp_offset and gp_sp_offset's calculation method,
            when frame->mask or frame->fmask is zero, don't minus UNITS_PER_WORD
            or UNITS_PER_FP_REG.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/loongarch/prolog-opt.c: New test.
    
    (cherry picked from commit aa8fd7f65683ef9c3b6d2e9306bea2f28b5cadf7)

Diff:
---
 gcc/config/loongarch/loongarch.cc               | 12 +++++++++---
 gcc/testsuite/gcc.target/loongarch/prolog-opt.c | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index d72b256df51..5c9a33c14f7 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -917,8 +917,12 @@ loongarch_compute_frame_info (void)
   frame->frame_pointer_offset = offset;
   /* Next are the callee-saved FPRs.  */
   if (frame->fmask)
-    offset += LARCH_STACK_ALIGN (num_f_saved * UNITS_PER_FP_REG);
-  frame->fp_sp_offset = offset - UNITS_PER_FP_REG;
+    {
+      offset += LARCH_STACK_ALIGN (num_f_saved * UNITS_PER_FP_REG);
+      frame->fp_sp_offset = offset - UNITS_PER_FP_REG;
+    }
+  else
+    frame->fp_sp_offset = offset;
   /* Next are the callee-saved GPRs.  */
   if (frame->mask)
     {
@@ -931,8 +935,10 @@ loongarch_compute_frame_info (void)
 	frame->save_libcall_adjustment = x_save_size;
 
       offset += x_save_size;
+      frame->gp_sp_offset = offset - UNITS_PER_WORD;
     }
-  frame->gp_sp_offset = offset - UNITS_PER_WORD;
+  else
+    frame->gp_sp_offset = offset;
   /* The hard frame pointer points above the callee-saved GPRs.  */
   frame->hard_frame_pointer_offset = offset;
   /* Above the hard frame pointer is the callee-allocated varags save area.  */
diff --git a/gcc/testsuite/gcc.target/loongarch/prolog-opt.c b/gcc/testsuite/gcc.target/loongarch/prolog-opt.c
new file mode 100644
index 00000000000..0470a1f1eee
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/prolog-opt.c
@@ -0,0 +1,15 @@
+/* Test that LoongArch backend stack drop operation optimized.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -mabi=lp64d" } */
+/* { dg-final { scan-assembler "addi.d\t\\\$r3,\\\$r3,-16" } } */
+
+extern int printf (char *, ...);
+
+int main()
+{
+  char buf[1024 * 12];
+  printf ("%p\n", buf);
+  return 0;
+}
+