[PATCH 2/2] or1k: Improve If-Conversion by delaying cbranch splits

[Stafford Horne <shorne@gmail.com>]

When working on PR120587 I found that the ce1 pass was not able to
properly optimize branches on OpenRISC.  This is because of the early
splitting of "compare" and "branch" instructions during the expand pass.

Convert the cbranch* instructions from define_expand to
define_insn_and_split.  This dalays the instruction split until after
the ce1 pass is done giving ce1 the best opportunity to perform the
optimizations on the original form of cbranch<mode>4 instructions.

gcc/ChangeLog:

	* config/or1k/or1k.cc (or1k_noce_conversion_profitable_p): New
	function.
	(or1k_is_cmov_insn): New function.
	(TARGET_NOCE_CONVERSION_PROFITABLE_P): Define macro.
	* config/or1k/or1k.md (cbranchsi4): Convert to insn_and_split.
	(cbranch<mode>4): Convert to insn_and_split.

Signed-off-by: Stafford Horne <shorne@gmail.com>
---
 gcc/config/or1k/or1k.cc | 54 +++++++++++++++++++++++++++++++++++++++++
 gcc/config/or1k/or1k.md | 32 ++++++++++++++++++++++--
 2 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/gcc/config/or1k/or1k.cc b/gcc/config/or1k/or1k.cc
index f1c92c6bf6c..36c16a51d44 100644
--- a/gcc/config/or1k/or1k.cc
+++ b/gcc/config/or1k/or1k.cc
@@ -1654,6 +1654,60 @@ or1k_rtx_costs (rtx x, machine_mode mode, int outer_code, int /* opno */,
 #undef TARGET_RTX_COSTS
 #define TARGET_RTX_COSTS or1k_rtx_costs
 
+static bool
+or1k_is_cmov_insn (rtx_insn *seq)
+{
+  rtx_insn *curr_insn = seq;
+  rtx set = NULL_RTX;
+
+  /* The pattern may start with a simple set with register operands.  Skip
+     through any of those.  */
+  while (curr_insn)
+    {
+      set = single_set (curr_insn);
+      if (!set
+	  || !REG_P (SET_DEST (set)))
+	return false;
+
+      /* If it's not a simple reg or immediate break.  */
+      if (REG_P (SET_SRC (set)) || CONST_INT_P (SET_SRC (set)))
+        curr_insn = NEXT_INSN (curr_insn);
+      else
+	break;
+    }
+
+  /* The next instruction should be a compare.  OpenRISC has many operators used
+     for comparison so skip and confirm the next is IF_THEN_ELSE.  */
+  curr_insn = NEXT_INSN (curr_insn);
+  if (!curr_insn)
+    return false;
+
+  /* And the last instruction should be an IF_THEN_ELSE.  */
+  set = single_set (curr_insn);
+  if (!set
+      || !REG_P (SET_DEST (set))
+      || GET_CODE (SET_SRC (set)) != IF_THEN_ELSE)
+    return false;
+
+  return !NEXT_INSN (curr_insn);
+}
+
+/* Implement TARGET_NOCE_CONVERSION_PROFITABLE_P.  We detect if the conversion
+   resulted in a l.cmov instruction and if so we consider it more profitable than
+   branch instructions.  */
+
+static bool
+or1k_noce_conversion_profitable_p (rtx_insn *seq,
+				    struct noce_if_info *if_info)
+{
+  if (TARGET_CMOV)
+    return or1k_is_cmov_insn (seq);
+
+  return default_noce_conversion_profitable_p (seq, if_info);
+}
+
+#undef TARGET_NOCE_CONVERSION_PROFITABLE_P
+#define TARGET_NOCE_CONVERSION_PROFITABLE_P or1k_noce_conversion_profitable_p
 
 /* A subroutine of the atomic operation splitters.  Jump to LABEL if
    COND is true.  Mark the jump as unlikely to be taken.  */
diff --git a/gcc/config/or1k/or1k.md b/gcc/config/or1k/or1k.md
index a30cc18892d..bf7125375ac 100644
--- a/gcc/config/or1k/or1k.md
+++ b/gcc/config/or1k/or1k.md
@@ -609,7 +609,7 @@
 ;; Branch instructions
 ;; -------------------------------------------------------------------------
 
-(define_expand "cbranchsi4"
+(define_insn_and_split "cbranchsi4"
   [(set (pc)
 	(if_then_else
 	  (match_operator 0 "comparison_operator"
@@ -618,13 +618,27 @@
 	  (label_ref (match_operand 3 "" ""))
 	  (pc)))]
   ""
+  "#"
+  "&& 1"
+  [(const_int 0)]
 {
+  rtx label;
+
+  /* Generate *scc */
   or1k_expand_compare (operands);
+  /* Generate *cbranch */
+  label = gen_rtx_LABEL_REF (VOIDmode, operands[3]);
+  emit_jump_insn (gen_rtx_SET (pc_rtx,
+			       gen_rtx_IF_THEN_ELSE (VOIDmode,
+						     operands[0],
+						     label,
+						     pc_rtx)));
+  DONE;
 })
 
 ;; Support FP branching
 
-(define_expand "cbranch<F:mode>4"
+(define_insn_and_split "cbranch<F:mode>4"
   [(set (pc)
 	(if_then_else
 	  (match_operator 0 "fp_comparison_operator"
@@ -633,8 +647,22 @@
 	  (label_ref (match_operand 3 "" ""))
 	  (pc)))]
   "TARGET_HARD_FLOAT"
+  "#"
+  "&& 1"
+  [(const_int 0)]
 {
+  rtx label;
+
+  /* Generate *scc */
   or1k_expand_compare (operands);
+  /* Generate *cbranch */
+  label = gen_rtx_LABEL_REF (VOIDmode, operands[3]);
+  emit_jump_insn (gen_rtx_SET (pc_rtx,
+			       gen_rtx_IF_THEN_ELSE (VOIDmode,
+						     operands[0],
+						     label,
+						     pc_rtx)));
+  DONE;
 })
 
 (define_insn "*cbranch"
-- 
2.49.0