RISC-V: Fix backward_propagate_worthwhile_p

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (loop_basic_block_p): Adjust function.
	(backward_propagate_worthwhile_p): Fix non-worthwhile.

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 7933644..4d0e97d 100644 (file)
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -116,10 +116,27 @@ vlmax_avl_insn_p (rtx_insn *rinsn)
          || INSN_CODE (rinsn) == CODE_FOR_vlmax_avldi);
 }
 
+/* Return true if the block is a loop itself:
+         local_dem
+            __________
+        ____|____     |
+       |        |     |
+       |________|     |
+            |_________|
+         reaching_out
+*/
 static bool
 loop_basic_block_p (const basic_block cfg_bb)
 {
-  return JUMP_P (BB_END (cfg_bb)) && any_condjump_p (BB_END (cfg_bb));
+  if (JUMP_P (BB_END (cfg_bb)) && any_condjump_p (BB_END (cfg_bb)))
+    {
+      edge e;
+      edge_iterator ei;
+      FOR_EACH_EDGE (e, ei, cfg_bb->succs)
+       if (e->dest->index == cfg_bb->index)
+         return true;
+    }
+  return false;
 }
 
 /* Return true if it is an RVV instruction depends on VTYPE global
@@ -271,26 +288,60 @@ backward_propagate_worthwhile_p (const basic_block cfg_bb,
 {
   if (loop_basic_block_p (cfg_bb))
     {
-      if (block_info.local_dem.compatible_p (block_info.reaching_out))
-       return true;
-
-      /* There is a obvious case that is not worthwhile and meaningless
-        to propagate the demand information:
-                         local_dem
-                            __________
-                        ____|____     |
-                       |        |     |
-                       |________|     |
-                            |_________|
-                         reaching_out
-         Header is incompatible with reaching_out and the block is loop itself,
-         we don't backward propagate the local_dem since we can't avoid emit
-         vsetvl for the local_dem.  */
-      edge e;
-      edge_iterator ei;
-      FOR_EACH_EDGE (e, ei, cfg_bb->succs)
-       if (e->dest->index == cfg_bb->index)
+      if (block_info.reaching_out.valid_or_dirty_p ())
+       {
+         if (block_info.local_dem.compatible_p (block_info.reaching_out))
+           {
+             /* Case 1 (Can backward propagate):
+                ....
+                bb0:
+                ...
+                for (int i = 0; i < n; i++)
+                  {
+                    vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i + 5, 7);
+                    __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
+                  }
+                The local_dem is compatible with reaching_out. Such case is
+                worthwhile backward propagation.  */
+             return true;
+           }
+         else
+           {
+             /* Case 2 (Don't backward propagate):
+                   ....
+                   bb0:
+                   ...
+                   for (int i = 0; i < n; i++)
+                     {
+                       vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i + 5, 7);
+                       __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
+                       vint16mf2_t v2 = __riscv_vle16_v_i16mf2 (in + i + 6, 8);
+                       __riscv_vse16_v_i16mf2 (out + i + 6, v, 8);
+                     }
+                The local_dem is incompatible with reaching_out.
+                It makes no sense to backward propagate the local_dem since we
+                can't avoid VSETVL inside the loop.  */
+             return false;
+           }
+       }
+      else
+       {
+         gcc_assert (block_info.reaching_out.unknown_p ());
+         /* Case 3 (Don't backward propagate):
+               ....
+               bb0:
+               ...
+               for (int i = 0; i < n; i++)
+                 {
+                   vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i + 5, 7);
+                   __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
+                   fn3 ();
+                 }
+           The local_dem is VALID, but the reaching_out is UNKNOWN.
+           It makes no sense to backward propagate the local_dem since we
+           can't avoid VSETVL inside the loop.  */
          return false;
+       }
     }
 
   return true;