RISC-V: Enforce atomic compare_exchange SEQ_CST

This patch enforces SEQ_CST for atomic compare_exchange ops.

Replace Fence/LR.aq/SC.aq pairs with SEQ_CST LR.aqrl/SC.rl pairs
recommended by table A.6 of the ISA manual.

2023-04-27 Patrick O'Neill <patrick@rivosinc.com>

gcc/ChangeLog:

	* config/riscv/sync.md (atomic_cas_value_strong<mode>): Change
	FENCE/LR.aq/SC.aq into sequentially consistent LR.aqrl/SC.rl
	pair.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>

diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index 0c83ef04607096a65fe7c9505e6b3f79804a5be4..5620d6ffa5871db15ea8890fc258980e381bcf90 100644 (file)
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -297,9 +297,16 @@
         UNSPEC_COMPARE_AND_SWAP))
    (clobber (match_scratch:GPR 6 "=&r"))]
   "TARGET_ATOMIC"
-  "%F5 1: lr.<amo>%A5 %0,%1; bne %0,%z2,1f; sc.<amo>%A4 %6,%z3,%1; bnez %6,1b; 1:"
+  {
+    return "1:\;"
+          "lr.<amo>.aqrl\t%0,%1\;"
+          "bne\t%0,%z2,1f\;"
+          "sc.<amo>.rl\t%6,%z3,%1\;"
+          "bnez\t%6,1b\;"
+          "1:";
+  }
   [(set_attr "type" "atomic")
-   (set (attr "length") (const_int 20))])
+   (set (attr "length") (const_int 16))])
 
 (define_expand "atomic_compare_and_swap<mode>"
   [(match_operand:SI 0 "register_operand" "")   ;; bool output