Re: [path] PR 54900: store data race in if-conversion pass

[Aldy Hernandez]

On 10/16/12 23:21, Jeff Law wrote:

On 10/16/2012 07:51 PM, Richard Henderson wrote:

On 2012-10-17 09:53, Aldy Hernandez wrote:

+/* Like memory_modified_in_insn_p, but return TRUE if INSN will
+   *SURELY* modify the memory contents of MEM.  */
+bool
+memory_surely_modified_in_insn_p (const_rtx mem, const_rtx insn)

I don't like the word "surely".  Are we certain or not?

It's longer, but perhaps "definitely" or "must_be"?

I'd go with "must_be" or something similar.  "must" is pretty common
terminology when talking about aliasing properties.

jeff

must_be it is.

Committed the patch below.

Thanks.

        PR rtl-optimization/54900
        * ifcvt.c (noce_can_store_speculate_p): Call
        memory_must_be_modified_in_insn_p.
        * alias.c (memory_must_be_modified_in_insn_p): New.
        (set_dest_equal_p): New.
        * rtl.h (memory_must_be_modified_in_p): Protoize.
    
diff --git a/gcc/alias.c b/gcc/alias.c
index 244ca52..c5e6417 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -2762,6 +2762,39 @@ memory_modified_in_insn_p (const_rtx mem, const_rtx insn)
   return memory_modified;
 }
 
+/* Return TRUE if the destination of a set is rtx identical to
+   ITEM.  */
+static inline bool
+set_dest_equal_p (const_rtx set, const_rtx item)
+{
+  rtx dest = SET_DEST (set);
+  return rtx_equal_p (dest, item);
+}
+
+/* Like memory_modified_in_insn_p, but return TRUE if INSN will
+   *DEFINITELY* modify the memory contents of MEM.  */
+bool
+memory_must_be_modified_in_insn_p (const_rtx mem, const_rtx insn)
+{
+  if (!INSN_P (insn))
+    return false;
+  insn = PATTERN (insn);
+  if (GET_CODE (insn) == SET)
+    return set_dest_equal_p (insn, mem);
+  else if (GET_CODE (insn) == PARALLEL)
+    {
+      int i;
+      for (i = 0; i < XVECLEN (insn, 0); i++)
+       {
+         rtx sub = XVECEXP (insn, 0, i);
+         if (GET_CODE (sub) == SET
+             &&  set_dest_equal_p (sub, mem))
+           return true;
+       }
+    }
+  return false;
+}
+
 /* Initialize the aliasing machinery.  Initialize the REG_KNOWN_VALUE
    array.  */
 
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 2f486a2..5654c66 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -2415,7 +2415,7 @@ noce_can_store_speculate_p (basic_block top_bb, const_rtx 
mem)
                  || (CALL_P (insn) && (!RTL_CONST_CALL_P (insn)))))
            return false;
 
-         if (memory_modified_in_insn_p (mem, insn))
+         if (memory_must_be_modified_in_insn_p (mem, insn))
            return true;
          if (modified_in_p (XEXP (mem, 0), insn))
            return false;
diff --git a/gcc/rtl.h b/gcc/rtl.h
index eeeb6ba..09f1e77 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -2616,6 +2616,7 @@ extern void init_alias_analysis (void);
 extern void end_alias_analysis (void);
 extern void vt_equate_reg_base_value (const_rtx, const_rtx);
 extern bool memory_modified_in_insn_p (const_rtx, const_rtx);
+extern bool memory_must_be_modified_in_insn_p (const_rtx, const_rtx);
 extern bool may_be_sp_based_p (rtx);
 extern rtx gen_hard_reg_clobber (enum machine_mode, unsigned int);
 extern rtx get_reg_known_value (unsigned int);