RISC-V: Eliminate AMO op fences

Atomic operations with the appropriate bits set already enfore release
semantics. Remove unnecessary release fences from atomic ops.

This change brings AMO ops in line with table A.6 of the ISA manual.

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

gcc/ChangeLog:

	* config/riscv/riscv.cc
	(riscv_memmodel_needs_amo_release): Change function name.
	(riscv_print_operand): Remove unneeded %F case.
	* config/riscv/sync.md: Remove unneeded fences.

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

2 files changed, 11 insertions, 17 deletions

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index f8bc402..ce79c9b 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -4317,11 +4317,11 @@ riscv_memmodel_needs_amo_acquire (enum memmodel model)
     }
 }
 
-/* Return true if a FENCE should be emitted to before a memory access to
-   implement the release portion of memory model MODEL.  */
+/* Return true if the .RL suffix should be added to an AMO to implement the
+   release portion of memory model MODEL.  */
 
 static bool
-riscv_memmodel_needs_release_fence (enum memmodel model)
+riscv_memmodel_needs_amo_release (enum memmodel model)
 {
   switch (model)
     {
@@ -4347,7 +4347,6 @@ riscv_memmodel_needs_release_fence (enum memmodel model)
    'R'	Print the low-part relocation associated with OP.
    'C'	Print the integer branch condition for comparison OP.
    'A'	Print the atomic operation suffix for memory model OP.
-   'F'	Print a FENCE if the memory model requires a release.
    'z'	Print x0 if OP is zero, otherwise print OP normally.
    'i'	Print i if the operand is not a register.
    'S'	Print shift-index of single-bit mask OP.
@@ -4509,19 +4508,14 @@ riscv_print_operand (FILE *file, rtx op, int letter)
 
     case 'A':
       if (riscv_memmodel_needs_amo_acquire (model)
-	  && riscv_memmodel_needs_release_fence (model))
+	  && riscv_memmodel_needs_amo_release (model))
 	fputs (".aqrl", file);
       else if (riscv_memmodel_needs_amo_acquire (model))
 	fputs (".aq", file);
-      else if (riscv_memmodel_needs_release_fence (model))
+      else if (riscv_memmodel_needs_amo_release (model))
 	fputs (".rl", file);
       break;
 
-    case 'F':
-      if (riscv_memmodel_needs_release_fence (model))
-	fputs ("fence iorw,ow; ", file);
-      break;
-
     case 'i':
       if (code != REG)
         fputs ("i", file);
diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index 1acb78a..9a3b57b 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -91,9 +91,9 @@
 	   (match_operand:SI 2 "const_int_operand")] ;; model
 	 UNSPEC_SYNC_OLD_OP))]
   "TARGET_ATOMIC"
-  "%F2amo<insn>.<amo>%A2 zero,%z1,%0"
+  "amo<insn>.<amo>%A2\tzero,%z1,%0"
   [(set_attr "type" "atomic")
-   (set (attr "length") (const_int 8))])
+   (set (attr "length") (const_int 4))])
 
 (define_insn "atomic_fetch_<atomic_optab><mode>"
   [(set (match_operand:GPR 0 "register_operand" "=&r")
@@ -105,9 +105,9 @@
 	   (match_operand:SI 3 "const_int_operand")] ;; model
 	 UNSPEC_SYNC_OLD_OP))]
   "TARGET_ATOMIC"
-  "%F3amo<insn>.<amo>%A3 %0,%z2,%1"
+  "amo<insn>.<amo>%A3\t%0,%z2,%1"
   [(set_attr "type" "atomic")
-   (set (attr "length") (const_int 8))])
+   (set (attr "length") (const_int 4))])
 
 (define_insn "subword_atomic_fetch_strong_<atomic_optab>"
   [(set (match_operand:SI 0 "register_operand" "=&r")		   ;; old value at mem
@@ -247,9 +247,9 @@
    (set (match_dup 1)
 	(match_operand:GPR 2 "register_operand" "0"))]
   "TARGET_ATOMIC"
-  "%F3amoswap.<amo>%A3 %0,%z2,%1"
+  "amoswap.<amo>%A3\t%0,%z2,%1"
   [(set_attr "type" "atomic")
-   (set (attr "length") (const_int 8))])
+   (set (attr "length") (const_int 4))])
 
 (define_expand "atomic_exchange<mode>"
   [(match_operand:SHORT 0 "register_operand") ;; old value at mem