[PATCH] rx: avoid adding setpsw for rx_cmpstrn when len is const

[Keith Packard]

We can avoid the setpsw instructions when len is a known constant.
When len is zero, the insn result is zero. When len is non-zero,
the scmpu instructions will set the flags correctly.

Signed-off-by: Keith Packard <kei...@keithp.com>
---
 gcc/config/rx/rx.md | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/gcc/config/rx/rx.md b/gcc/config/rx/rx.md
index edb2c96603f..8c7974d69a5 100644
--- a/gcc/config/rx/rx.md
+++ b/gcc/config/rx/rx.md
@@ -2545,6 +2545,16 @@ (define_expand "cmpstrnsi"
    (match_operand:SI                            4 "immediate_operand")] ;; 
Known Align
   "rx_allow_string_insns"
   {
+    bool const_len = CONST_INT_P(operands[3]);
+    if (const_len)
+    {
+      if (INTVAL(operands[3]) == 0)
+      {
+        emit_move_insn (operands[0], operands[3]);
+        DONE;
+      }
+    }
+
     rtx str1 = gen_rtx_REG (SImode, 1);
     rtx str2 = gen_rtx_REG (SImode, 2);
     rtx len  = gen_rtx_REG (SImode, 3);
@@ -2553,6 +2563,11 @@ (define_expand "cmpstrnsi"
     emit_move_insn (str2, force_operand (XEXP (operands[2], 0), NULL_RTX));
     emit_move_insn (len, operands[3]);
 
+    /* Set flags in case len is zero */
+    if (!const_len) {
+      emit_insn (gen_setpsw (GEN_INT('C')));
+      emit_insn (gen_setpsw (GEN_INT('Z')));
+    }
     emit_insn (gen_rx_cmpstrn (operands[0], operands[1], operands[2]));
     DONE;
   }
@@ -2590,9 +2605,7 @@ (define_insn "rx_cmpstrn"
    (clobber (reg:SI 3))
    (clobber (reg:CC CC_REG))]
   "rx_allow_string_insns"
-  "setpsw  z           ; Set flags in case len is zero
-   setpsw  c
-   scmpu               ; Perform the string comparison
+  "scmpu               ; Perform the string comparison
    mov     #-1, %0      ; Set up -1 result (which cannot be created
                         ; by the SC insn)
    bnc    ?+           ; If Carry is not set skip over
-- 
2.47.2