[gcc(refs/users/guojiufu/heads/personal-branch)] amdgcn: Add fold_left_plus vector reductions

[Jiu Fu Guo]

https://gcc.gnu.org/g:bf628a97efaf11204ab02527b30ca71d7759ca37

commit bf628a97efaf11204ab02527b30ca71d7759ca37
Author: Andrew Stubbs <ams@codesourcery.com>
Date:   Mon Feb 10 13:23:29 2020 +0000

    amdgcn: Add fold_left_plus vector reductions
    
    These aren't real in-order instructions, because the ISA can't do that
    quickly, but a means to allow regular out-of-order reductions when that's
    good enough, but the middle-end doesn't know so.
    
            gcc/
            * config/gcn/gcn-valu.md (fold_left_plus_<mode>): New.

Diff:
---
 gcc/config/gcn/gcn-valu.md | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/gcc/config/gcn/gcn-valu.md b/gcc/config/gcn/gcn-valu.md
index 6d7fecaa12c..26559ff765e 100644
--- a/gcc/config/gcn/gcn-valu.md
+++ b/gcc/config/gcn/gcn-valu.md
@@ -3076,6 +3076,26 @@
     DONE;
   })
 
+;; Warning: This "-ffast-math" implementation converts in-order reductions
+;;          into associative reductions. It's also used where OpenMP or
+;;          OpenACC paralellization has already broken the in-order semantics.
+(define_expand "fold_left_plus_<mode>"
+ [(match_operand:<SCALAR_MODE> 0 "register_operand")
+  (match_operand:<SCALAR_MODE> 1 "gcn_alu_operand")
+  (match_operand:V_FP 2 "gcn_alu_operand")]
+  "can_create_pseudo_p ()
+   && (flag_openacc || flag_openmp
+       || flag_associative_math)"
+  {
+    rtx dest = operands[0];
+    rtx scalar = operands[1];
+    rtx vector = operands[2];
+    rtx tmp = gen_reg_rtx (<SCALAR_MODE>mode);
+
+    emit_insn (gen_reduc_plus_scal_<mode> (tmp, vector));
+    emit_insn (gen_add<scalar_mode>3 (dest, scalar, tmp));
+     DONE;
+   })
 
 (define_insn "*<reduc_op>_dpp_shr_<mode>"
   [(set (match_operand:V_1REG 0 "register_operand"   "=v")