[PATCH v3] LoongArch: Modify fp_sp_offset and gp_sp_offset's calculation method when frame->mask or frame->fmask is zero.

Lulu Cheng chenglulu@loongson.cn
Thu Jul 7 10:30:50 GMT 2022


update testsuite.

--------------------------

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.
---
 gcc/config/loongarch/loongarch.cc               | 12 +++++++++---
 gcc/testsuite/gcc.target/loongarch/prolog-opt.c | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/loongarch/prolog-opt.c

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..c7bd71dde93
--- /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" } } */
+
+#include <stdio.h>
+
+int main()
+{
+  char buf[1024 * 12];
+  printf ("%p\n", buf);
+  return 0;
+}
+
-- 
2.31.1



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