RISC-V: Optimize RVV epilogue logic.

Sometimes "step1 -= scalable_frame" will cause adjust equal to
zero. And it will generate additional redundant instruction
"addi sp,sp,0". Add checking segement to skip that case.

This testcase mix exist spill-1.c and adding new fun to check if
there have redundant addi intructions. Idea provided by Jeff Law.

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_expand_epilogue):
	Do not emit useless add sp, sp, 0 instrutions.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/spill-sp-adjust.c: New test.

2 files changed, 32 insertions, 15 deletions

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index e36ff05..ed8ba83 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -5204,25 +5204,29 @@ riscv_expand_epilogue (int style)
 	  step1 -= scalable_frame;
 	}
 
-      /* Get an rtx for STEP1 that we can add to BASE.  */
-      rtx adjust = GEN_INT (step1.to_constant ());
-      if (!SMALL_OPERAND (step1.to_constant ()))
+      /* Get an rtx for STEP1 that we can add to BASE.
+	 Skip if adjust equal to zero.  */
+      if (step1.to_constant () != 0)
 	{
-	  riscv_emit_move (RISCV_PROLOGUE_TEMP (Pmode), adjust);
-	  adjust = RISCV_PROLOGUE_TEMP (Pmode);
-	}
-
-      insn = emit_insn (
-	       gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx, adjust));
+	  rtx adjust = GEN_INT (step1.to_constant ());
+	  if (!SMALL_OPERAND (step1.to_constant ()))
+	    {
+	      riscv_emit_move (RISCV_PROLOGUE_TEMP (Pmode), adjust);
+	      adjust = RISCV_PROLOGUE_TEMP (Pmode);
+	    }
 
-      rtx dwarf = NULL_RTX;
-      rtx cfa_adjust_rtx = gen_rtx_PLUS (Pmode, stack_pointer_rtx,
-					 GEN_INT (step2));
+	  insn = emit_insn (gen_add3_insn (stack_pointer_rtx,
+					   stack_pointer_rtx,
+					   adjust));
+	  rtx dwarf = NULL_RTX;
+	  rtx cfa_adjust_rtx = gen_rtx_PLUS (Pmode, stack_pointer_rtx,
+					     GEN_INT (step2));
 
-      dwarf = alloc_reg_note (REG_CFA_DEF_CFA, cfa_adjust_rtx, dwarf);
-      RTX_FRAME_RELATED_P (insn) = 1;
+	  dwarf = alloc_reg_note (REG_CFA_DEF_CFA, cfa_adjust_rtx, dwarf);
+	  RTX_FRAME_RELATED_P (insn) = 1;
 
-      REG_NOTES (insn) = dwarf;
+	  REG_NOTES (insn) = dwarf;
+	}
     }
   else if (frame_pointer_needed)
     {
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/spill-sp-adjust.c b/gcc/testsuite/gcc.target/riscv/rvv/base/spill-sp-adjust.c
new file mode 100644
index 0000000..f8c9f63
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/spill-sp-adjust.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv" } */
+
+#include "spill-1.c"
+
+void
+spill_sp_adjust (int8_t *v)
+{
+  vint8mf8_t v1 = *(vint8mf8_t*)v; 
+}
+
+/* Make sure we do not have a useless SP adjustment.  */
+/* { dg-final { scan-assembler-not "addi\tsp,sp,0" } } */