[gcc r13-7581] RISC-V: Bugfix for riscv-vsetvl pass.

[gcc r13-7581] RISC-V: Bugfix for riscv-vsetvl pass.

[Pan Li]

https://gcc.gnu.org/g:a1322d76ca1c3c914fb818d9ba3edc291ccfa25e

commit r13-7581-ga1322d76ca1c3c914fb818d9ba3edc291ccfa25e
Author: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
Date:   Sun Jul 16 08:31:22 2023 +0800

    RISC-V: Bugfix for riscv-vsetvl pass.
    
    This patch comes from part of below change, which locate one bug of rvv
    vsetvel pass when auto-vectorization.
    
    https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624523.html
    
    Unforunately, It is not easy to reproduce this bug by intrinsic APIs
    but it is worth to backport to GCC 13.
    
    Signed-off-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
    
    gcc/ChangeLog:
    
            * config/riscv/riscv-vsetvl.cc (gen_vsetvl_pat): Add vl parameter.
            (change_vsetvl_insn): Ditto.
            (change_insn): Add validate change as well as assert.
            (pass_vsetvl::backward_demand_fusion): Allow forward.

Diff:
---
 gcc/config/riscv/riscv-vsetvl.cc | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 3355ca4e3fb..fbd26988106 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -633,7 +633,8 @@ gen_vsetvl_pat (enum vsetvl_type insn_type, const vl_vtype_info &info, rtx vl)
 }
 
 static rtx
-gen_vsetvl_pat (rtx_insn *rinsn, const vector_insn_info &info)
+gen_vsetvl_pat (rtx_insn *rinsn, const vector_insn_info &info,
+		rtx vl = NULL_RTX)
 {
   rtx new_pat;
   vl_vtype_info new_info = info;
@@ -644,7 +645,7 @@ gen_vsetvl_pat (rtx_insn *rinsn, const vector_insn_info &info)
   if (vsetvl_insn_p (rinsn) || vlmax_avl_p (info.get_avl ()))
     {
       rtx dest = get_vl (rinsn);
-      new_pat = gen_vsetvl_pat (VSETVL_NORMAL, new_info, dest);
+      new_pat = gen_vsetvl_pat (VSETVL_NORMAL, new_info, vl ? vl : dest);
     }
   else if (INSN_CODE (rinsn) == CODE_FOR_vsetvl_vtype_change_only)
     new_pat = gen_vsetvl_pat (VSETVL_VTYPE_CHANGE_ONLY, new_info, NULL_RTX);
@@ -926,7 +927,8 @@ change_insn (rtx_insn *rinsn, rtx new_pat)
       print_rtl_single (dump_file, PATTERN (rinsn));
     }
 
-  validate_change (rinsn, &PATTERN (rinsn), new_pat, false);
+  bool change_p = validate_change (rinsn, &PATTERN (rinsn), new_pat, false);
+  gcc_assert (change_p);
 
   if (dump_file)
     {
@@ -1039,7 +1041,8 @@ change_insn (function_info *ssa, insn_change change, insn_info *insn,
 }
 
 static void
-change_vsetvl_insn (const insn_info *insn, const vector_insn_info &info)
+change_vsetvl_insn (const insn_info *insn, const vector_insn_info &info,
+		    rtx vl = NULL_RTX)
 {
   rtx_insn *rinsn;
   if (vector_config_insn_p (insn->rtl ()))
@@ -1053,7 +1056,7 @@ change_vsetvl_insn (const insn_info *insn, const vector_insn_info &info)
       rinsn = PREV_INSN (insn->rtl ());
       gcc_assert (vector_config_insn_p (rinsn));
     }
-  rtx new_pat = gen_vsetvl_pat (rinsn, info);
+  rtx new_pat = gen_vsetvl_pat (rinsn, info, vl);
   change_insn (rinsn, new_pat);
 }
 
@@ -3331,7 +3334,21 @@ pass_vsetvl::backward_demand_fusion (void)
 				       new_info))
 		continue;
 
-	      change_vsetvl_insn (new_info.get_insn (), new_info);
+	      rtx vl = NULL_RTX;
+	      /* Backward VLMAX VL:
+		   bb 3:
+		     vsetivli zero, 1 ... -> vsetvli t1, zero
+		     vmv.s.x
+		   bb 5:
+		     vsetvli t1, zero ... -> to be elided.
+		     vlse16.v
+
+		   We should forward "t1".  */
+	      if (!block_info.reaching_out.has_avl_reg ()
+		&& vlmax_avl_p (new_info.get_avl ()))
+		vl = get_vl (prop.get_insn ()->rtl ());
+	     change_vsetvl_insn (new_info.get_insn (), new_info, vl);
+
 	      if (block_info.local_dem == block_info.reaching_out)
 		block_info.local_dem = new_info;
 	      block_info.reaching_out = new_info;