RISCV: Add -m(no)-omit-leaf-frame-pointer support.

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_save_reg_p): Save ra for leaf
	when enabling -mno-omit-leaf-frame-pointer
	(riscv_option_override): Override omit-frame-pointer.
	(riscv_frame_pointer_required): Save s0 for non-leaf function
	(TARGET_FRAME_POINTER_REQUIRED): Override defination
	* config/riscv/riscv.opt: Add option support.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/omit-frame-pointer-1.c: New test.
	* gcc.target/riscv/omit-frame-pointer-2.c: New test.
	* gcc.target/riscv/omit-frame-pointer-3.c: New test.
	* gcc.target/riscv/omit-frame-pointer-4.c: New test.
	* gcc.target/riscv/omit-frame-pointer-test.c: New test.

Signed-off-by: Yanzhang Wang <yanzhang.wang@intel.com>

gcc/config/riscv/riscv.cc

@@ -404,6 +404,10 @@ static const struct riscv_tune_info riscv_tune_info_table[] = {
 #include "riscv-cores.def"
 };
 
+/* Global variable to distinguish whether we should save and restore s0/fp for
+   function.  */
+static bool riscv_save_frame_pointer;
+
 void riscv_frame_info::reset(void)
 {
   total_size = 0;
@@ -5079,7 +5083,11 @@ riscv_save_reg_p (unsigned int regno)
   if (regno == HARD_FRAME_POINTER_REGNUM && frame_pointer_needed)
     return true;
 
-  if (regno == RETURN_ADDR_REGNUM && crtl->calls_eh_return)
+  /* Need not to use ra for leaf when frame pointer is turned off by option
+     whatever the omit-leaf-frame's value.  */
+  bool keep_leaf_ra = frame_pointer_needed && crtl->is_leaf
+    && !TARGET_OMIT_LEAF_FRAME_POINTER;
+  if (regno == RETURN_ADDR_REGNUM && (crtl->calls_eh_return || keep_leaf_ra))
     return true;
 
   /* If this is an interrupt handler, then must save extra registers.  */
@@ -6714,6 +6722,21 @@ riscv_option_override (void)
   if (flag_pic)
     riscv_cmodel = CM_PIC;
 
+  /* We need to save the fp with ra for non-leaf functions with no fp and ra
+     for leaf functions while no-omit-frame-pointer with
+     omit-leaf-frame-pointer.  The x_flag_omit_frame_pointer has the first
+     priority to determine whether the frame pointer is needed.  If we do not
+     override it, the fp and ra will be stored for leaf functions, which is not
+     our wanted.  */
+  riscv_save_frame_pointer = false;
+  if (TARGET_OMIT_LEAF_FRAME_POINTER_P (global_options.x_target_flags))
+    {
+      if (!global_options.x_flag_omit_frame_pointer)
+	riscv_save_frame_pointer = true;
+
+      global_options.x_flag_omit_frame_pointer = 1;
+    }
+
   /* We get better code with explicit relocs for CM_MEDLOW, but
      worse code for the others (for now).  Pick the best default.  */
   if ((target_flags_explicit & MASK_EXPLICIT_RELOCS) == 0)
@@ -8163,6 +8186,12 @@ riscv_preferred_else_value (unsigned, tree, unsigned int nops, tree *ops)
   return nops == 3 ? ops[2] : ops[0];
 }
 
+static bool
+riscv_frame_pointer_required (void)
+{
+  return riscv_save_frame_pointer && !crtl->is_leaf;
+}
+
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
 #define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
@@ -8467,6 +8496,9 @@ riscv_preferred_else_value (unsigned, tree, unsigned int nops, tree *ops)
 #undef TARGET_PREFERRED_ELSE_VALUE
 #define TARGET_PREFERRED_ELSE_VALUE riscv_preferred_else_value
 
+#undef TARGET_FRAME_POINTER_REQUIRED
+#define TARGET_FRAME_POINTER_REQUIRED riscv_frame_pointer_required
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-riscv.h"

gcc/config/riscv/riscv.opt

@@ -138,6 +138,10 @@ Enable the CSR checking for the ISA-dependent CRS and the read-only CSR.
 The ISA-dependent CSR are only valid when the specific ISA is set.  The
 read-only CSR can not be written by the CSR instructions.
 
+momit-leaf-frame-pointer
+Target Mask(OMIT_LEAF_FRAME_POINTER) Save
+Omit the frame pointer in leaf functions.
+
 Mask(64BIT)
 
 Mask(MUL)

gcc/testsuite/gcc.target/riscv/omit-frame-pointer-1.c

@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -fno-inline" } */
+
+#include "omit-frame-pointer-test.c"
+
+/* { dg-final { scan-assembler-times "sd\tra,\[0-9\]+\\(sp\\)" 2 } } */
+/* { dg-final { scan-assembler-times "sd\ts0,\[0-9\]+\\(sp\\)" 2 } } */

gcc/testsuite/gcc.target/riscv/omit-frame-pointer-2.c

@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2 -fno-omit-frame-pointer -momit-leaf-frame-pointer -fno-inline" } */
+
+#include "omit-frame-pointer-test.c"
+
+/* { dg-final { scan-assembler-times "sd\tra,\[0-9\]+\\(sp\\)" 1 } } */
+/* { dg-final { scan-assembler-times "sd\ts0,\[0-9\]+\\(sp\\)" 1 } } */

gcc/testsuite/gcc.target/riscv/omit-frame-pointer-3.c

@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2 -fomit-frame-pointer -mno-omit-leaf-frame-pointer -fno-inline" } */
+
+#include "omit-frame-pointer-test.c"
+
+/* { dg-final { scan-assembler-times "sd\tra,\[0-9\]+\\(sp\\)" 1 } } */
+/* { dg-final { scan-assembler-not "sd\ts0,\[0-9\]+\\(sp\\)"} } */

gcc/testsuite/gcc.target/riscv/omit-frame-pointer-4.c

@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2 -fomit-frame-pointer -momit-leaf-frame-pointer -fno-inline" } */
+
+#include "omit-frame-pointer-test.c"
+
+/* { dg-final { scan-assembler-times "sd\tra,\[0-9\]+\\(sp\\)" 1 } } */
+/* { dg-final { scan-assembler-not "sd\ts0,\[0-9\]+\\(sp\\)"} } */

gcc/testsuite/gcc.target/riscv/omit-frame-pointer-test.c

@@ -0,0 +1,13 @@
+int inc(int n)
+{
+  return n + 1;
+}
+
+
+int bar(void)
+{
+  int n = 100;
+  n = inc(n);
+  n = inc(n) + 100;
+  return n;
+}