RISC-V: Describe correct USEs for gpr_save pattern [PR95252]

- Verified on rv32emc/rv32gc/rv64gc bare-metal target and rv32gc/rv64gc
   linux target with qemu.

gcc/ChangeLog:

	* config/riscv/predicates.md (gpr_save_operation): New.
	* config/riscv/riscv-protos.h (riscv_gen_gpr_save_insn): New.
	(riscv_gpr_save_operation_p): Ditto.
	* config/riscv/riscv-sr.c (riscv_remove_unneeded_save_restore_calls):
	Ignore USEs for gpr_save patter.
	* config/riscv/riscv.c (gpr_save_reg_order): New.
	(riscv_expand_prologue): Use riscv_gen_gpr_save_insn to gen gpr_save.
	(riscv_gen_gpr_save_insn): New.
	(riscv_gpr_save_operation_p): Ditto.
	* config/riscv/riscv.md (S3_REGNUM): New.
	(S4_REGNUM): Ditto.
	(S5_REGNUM): Ditto.
	(S6_REGNUM): Ditto.
	(S7_REGNUM): Ditto.
	(S8_REGNUM): Ditto.
	(S9_REGNUM): Ditto.
	(S10_REGNUM): Ditto.
	(S11_REGNUM): Ditto.
	(gpr_save): Model USEs correctly.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/pr95252.c: New.

gcc/config/riscv/predicates.md

@@ -206,3 +206,9 @@
 
 (define_predicate "fp_branch_comparison"
   (match_code "unordered,ordered,unlt,unge,unle,ungt,uneq,ltgt,ne,eq,lt,le,gt,ge"))
+
+(define_special_predicate "gpr_save_operation"
+  (match_code "parallel")
+{
+  return riscv_gpr_save_operation_p (op);
+})

gcc/config/riscv/riscv-protos.h

@@ -73,6 +73,8 @@ extern bool riscv_can_use_return_insn (void);
 extern rtx riscv_function_value (const_tree, const_tree, enum machine_mode);
 extern bool riscv_expand_block_move (rtx, rtx, rtx);
 extern bool riscv_store_data_bypass_p (rtx_insn *, rtx_insn *);
+extern rtx riscv_gen_gpr_save_insn (struct riscv_frame_info *);
+extern bool riscv_gpr_save_operation_p (rtx);
 
 /* Routines implemented in riscv-c.c.  */
 void riscv_cpu_cpp_builtins (cpp_reader *);

gcc/config/riscv/riscv-sr.c

@@ -306,6 +306,10 @@ riscv_remove_unneeded_save_restore_calls (void)
 
 	  if (CALL_P (insn))
 	    ++call_count;
+	  /* Ignore any USEs in the gpr_save pattern.  They don't prevent us
+	     from optimizing away the save call.  */
+	  else if (insn == prologue_matched)
+	    ;
 	  else
 	    {
 	      df_ref use;

gcc/config/riscv/riscv.c

@@ -334,6 +334,14 @@ static const struct attribute_spec riscv_attribute_table[] =
   { NULL,	0,  0, false, false, false, false, NULL, NULL }
 };
 
+/* Order for the CLOBBERs/USEs of gpr_save.  */
+static const unsigned gpr_save_reg_order[] = {
+  INVALID_REGNUM, T0_REGNUM, T1_REGNUM, RETURN_ADDR_REGNUM,
+  S0_REGNUM, S1_REGNUM, S2_REGNUM, S3_REGNUM, S4_REGNUM,
+  S5_REGNUM, S6_REGNUM, S7_REGNUM, S8_REGNUM, S9_REGNUM,
+  S10_REGNUM, S11_REGNUM
+};
+
 /* A table describing all the processors GCC knows about.  */
 static const struct riscv_cpu_info riscv_cpu_info_table[] = {
   { "rocket", generic, &rocket_tune_info },
@@ -4069,9 +4077,9 @@ riscv_expand_prologue (void)
       rtx dwarf = NULL_RTX;
       dwarf = riscv_adjust_libcall_cfi_prologue ();
 
-      frame->mask = 0; /* Temporarily fib that we need not save GPRs.  */
       size -= frame->save_libcall_adjustment;
-      insn = emit_insn (gen_gpr_save (GEN_INT (mask)));
+      insn = emit_insn (riscv_gen_gpr_save_insn (frame));
+      frame->mask = 0; /* Temporarily fib that we need not save GPRs.  */
 
       RTX_FRAME_RELATED_P (insn) = 1;
       REG_NOTES (insn) = dwarf;
@@ -5177,6 +5185,77 @@ riscv_new_address_profitable_p (rtx memref, rtx_insn *insn, rtx new_addr)
   return new_cost <= old_cost;
 }
 
+/* Helper function for generating gpr_save pattern.  */
+
+rtx
+riscv_gen_gpr_save_insn (struct riscv_frame_info *frame)
+{
+  unsigned count = riscv_save_libcall_count (frame->mask);
+  /* 1 for unspec 2 for clobber t0/t1 and 1 for ra.  */
+  unsigned veclen = 1 + 2 + 1 + count;
+  rtvec vec = rtvec_alloc (veclen);
+
+  gcc_assert (veclen <= ARRAY_SIZE (gpr_save_reg_order));
+
+  RTVEC_ELT (vec, 0) =
+    gen_rtx_UNSPEC_VOLATILE (VOIDmode,
+      gen_rtvec (1, GEN_INT (frame->mask)), UNSPECV_GPR_SAVE);
+
+  for (int i = 1; i < veclen; ++i)
+    {
+      unsigned regno = gpr_save_reg_order[i];
+      rtx reg = gen_rtx_REG (Pmode, regno);
+      rtx elt;
+
+      /* t0 and t1 are CLOBBERs, others are USEs.  */
+      if (i < 3)
+	elt = gen_rtx_CLOBBER (Pmode, reg);
+      else
+	elt = gen_rtx_USE (Pmode, reg);
+
+      RTVEC_ELT (vec, i) = elt;
+    }
+
+  /* Largest number of caller-save register must set in mask if we are
+     not using __riscv_save_0.  */
+  gcc_assert ((count == 0) ||
+	      BITSET_P (frame->mask, gpr_save_reg_order[veclen - 1]));
+
+  return gen_rtx_PARALLEL (VOIDmode, vec);
+}
+
+/* Return true if it's valid gpr_save pattern.  */
+
+bool
+riscv_gpr_save_operation_p (rtx op)
+{
+  HOST_WIDE_INT len = XVECLEN (op, 0);
+  gcc_assert (len <= ARRAY_SIZE (gpr_save_reg_order));
+  for (int i = 0; i < len; i++)
+    {
+      rtx elt = XVECEXP (op, 0, i);
+      if (i == 0)
+	{
+	  /* First element in parallel is unspec.  */
+	  if (GET_CODE (elt) != UNSPEC_VOLATILE
+	      || GET_CODE (XVECEXP (elt, 0, 0)) != CONST_INT
+	      || XINT (elt, 1) != UNSPECV_GPR_SAVE)
+	    return false;
+	}
+      else
+	{
+	  /* Two CLOBBER and USEs, must check the order.  */
+	  unsigned expect_code = i < 3 ? CLOBBER : USE;
+	  if (GET_CODE (elt) != expect_code
+	      || !REG_P (XEXP (elt, 1))
+	      || (REGNO (XEXP (elt, 1)) != gpr_save_reg_order[i]))
+	    return false;
+	}
+	break;
+    }
+  return true;
+}
+
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
 #define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"

gcc/config/riscv/riscv.md

@@ -75,6 +75,15 @@
    (S0_REGNUM			8)
    (S1_REGNUM			9)
    (S2_REGNUM			18)
+   (S3_REGNUM			19)
+   (S4_REGNUM			20)
+   (S5_REGNUM			21)
+   (S6_REGNUM			22)
+   (S7_REGNUM			23)
+   (S8_REGNUM			24)
+   (S9_REGNUM			25)
+   (S10_REGNUM			26)
+   (S11_REGNUM			27)
 
    (NORMAL_RETURN		0)
    (SIBCALL_RETURN		1)
@@ -2427,10 +2436,14 @@
   ""
   "ebreak")
 
+;; Must use the registers that we save to prevent the rename reg optimization
+;; pass from using them before the gpr_save pattern when shrink wrapping
+;; occurs.  See bug 95252 for instance.
+
 (define_insn "gpr_save"
-  [(unspec_volatile [(match_operand 0 "const_int_operand")] UNSPECV_GPR_SAVE)
-   (clobber (reg:SI T0_REGNUM))
-   (clobber (reg:SI T1_REGNUM))]
+  [(match_parallel 1 "gpr_save_operation"
+     [(unspec_volatile [(match_operand 0 "const_int_operand")]
+	               UNSPECV_GPR_SAVE)])]
   ""
   { return riscv_output_gpr_save (INTVAL (operands[0])); })
 

gcc/testsuite/gcc.target/riscv/pr95252.c

@@ -0,0 +1,47 @@
+/* PR target/95252 */
+/* { dg-options "-O3 -funroll-loops -msave-restore" } */
+/* { dg-do run } */
+
+int a[6], b = 1, d, e;
+long long c;
+static int f = 1;
+
+void
+fn1 (int p1)
+{
+  b = (b >> 1) & (1 ^ a[(1 ^ p1) & 5]);
+}
+
+void
+fn2 ()
+{
+  b = (b >> 1) & (1 ^ a[(b ^ 1) & 1]);
+  fn1 (c >> 1 & 5);
+  fn1 (c >> 2 & 5);
+  fn1 (c >> 4 & 5);
+  fn1 (c >> 8 & 5);
+}
+
+int
+main ()
+{
+  int i, j;
+  for (; d;)
+    {
+      for (; e;)
+	fn2 ();
+      f = 0;
+    }
+  for (i = 0; i < 8; i++)
+    {
+      if (f)
+	i = 9;
+      for (j = 0; j < 7; j++)
+	fn2 ();
+    }
+
+  if (b != 0)
+    __builtin_abort ();
+
+  return 0;
+}