[PATCH] gimple-fold: Smarter optimization of _chk variants

Siddhesh Poyarekar siddhesh@gotplt.org
Wed Nov 10 09:38:36 GMT 2021


Instead of comparing LEN and SIZE only if they are constants, use their
ranges to decide if LEN will always be lower than or same as SIZE.

This change ends up putting the stringop-overflow warning line number
against the strcpy implementation, so adjust the warning check to be
line number agnostic.

gcc/ChangeLog:

	* gimple-fold.c (known_safe): New function.
	(gimple_fold_builtin_memory_chk, gimple_fold_builtin_stxcpy_chk,
	gimple_fold_builtin_stxncpy_chk,
	gimple_fold_builtin_snprintf_chk,
	gimple_fold_builtin_sprintf_chk): Use it.

gcc/testsuite/ChangeLog:

	* gcc.dg/Wobjsize-1.c: Make warning change line agnostic.
	* gcc.dg/builtin-chk-fold.c: New test.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
---
Testing:

- gcc.dg shows no new regressions on x86_64, a full bootstrap and test
  run are in progress.

 gcc/gimple-fold.c                       | 186 +++++++++---------------
 gcc/testsuite/gcc.dg/Wobjsize-1.c       |   5 +-
 gcc/testsuite/gcc.dg/builtin-chk-fold.c |  21 +++
 3 files changed, 94 insertions(+), 118 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/builtin-chk-fold.c

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 6e25a7c05db..7399b49d00f 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -2987,6 +2987,25 @@ gimple_fold_builtin_fputs (gimple_stmt_iterator *gsi,
   return false;
 }
 
+/* Return true if LEN is known to be less than or equal to SIZE at compile time
+   and false otherwise.  Emit a warning if LEN is known to be greater than SIZE
+   at compile time.  */
+
+static bool
+known_safe (gimple *stmt, tree len, tree size)
+{
+  if (len == NULL_TREE)
+    return false;
+
+  wide_int size_range[2];
+  wide_int len_range[2];
+  if (get_range (len, stmt, len_range) && get_range (size, stmt, size_range)
+      && wi::leu_p (len_range[1], size_range[0]))
+    return true;
+
+  return false;
+}
+
 /* Fold a call to the __mem{cpy,pcpy,move,set}_chk builtin.
    DEST, SRC, LEN, and SIZE are the arguments to the call.
    IGNORE is true, if return value can be ignored.  FCODE is the BUILT_IN_*
@@ -3024,39 +3043,24 @@ gimple_fold_builtin_memory_chk (gimple_stmt_iterator *gsi,
 	}
     }
 
-  if (! tree_fits_uhwi_p (size))
-    return false;
-
   tree maxlen = get_maxval_strlen (len, SRK_INT_VALUE);
-  if (! integer_all_onesp (size))
+  if (! integer_all_onesp (size)
+      && !known_safe (stmt, len, size) && !known_safe (stmt, maxlen, size))
     {
-      if (! tree_fits_uhwi_p (len))
+      /* MAXLEN and LEN both cannot be proved to be less than SIZE, at
+	 least try to optimize (void) __mempcpy_chk () into
+	 (void) __memcpy_chk () */
+      if (fcode == BUILT_IN_MEMPCPY_CHK && ignore)
 	{
-	  /* If LEN is not constant, try MAXLEN too.
-	     For MAXLEN only allow optimizing into non-_ocs function
-	     if SIZE is >= MAXLEN, never convert to __ocs_fail ().  */
-	  if (maxlen == NULL_TREE || ! tree_fits_uhwi_p (maxlen))
-	    {
-	      if (fcode == BUILT_IN_MEMPCPY_CHK && ignore)
-		{
-		  /* (void) __mempcpy_chk () can be optimized into
-		     (void) __memcpy_chk ().  */
-		  fn = builtin_decl_explicit (BUILT_IN_MEMCPY_CHK);
-		  if (!fn)
-		    return false;
+	  fn = builtin_decl_explicit (BUILT_IN_MEMCPY_CHK);
+	  if (!fn)
+	    return false;
 
-		  gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
-		  replace_call_with_call_and_fold (gsi, repl);
-		  return true;
-		}
-	      return false;
-	    }
+	  gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
+	  replace_call_with_call_and_fold (gsi, repl);
+	  return true;
 	}
-      else
-	maxlen = len;
-
-      if (tree_int_cst_lt (size, maxlen))
-	return false;
+      return false;
     }
 
   fn = NULL_TREE;
@@ -3126,61 +3130,47 @@ gimple_fold_builtin_stxcpy_chk (gimple_stmt_iterator *gsi,
       return true;
     }
 
-  if (! tree_fits_uhwi_p (size))
-    return false;
-
   tree maxlen = get_maxval_strlen (src, SRK_STRLENMAX);
   if (! integer_all_onesp (size))
     {
       len = c_strlen (src, 1);
-      if (! len || ! tree_fits_uhwi_p (len))
+      if (!known_safe (stmt, len, size) && !known_safe (stmt, maxlen, size))
 	{
-	  /* If LEN is not constant, try MAXLEN too.
-	     For MAXLEN only allow optimizing into non-_ocs function
-	     if SIZE is >= MAXLEN, never convert to __ocs_fail ().  */
-	  if (maxlen == NULL_TREE || ! tree_fits_uhwi_p (maxlen))
+	  if (fcode == BUILT_IN_STPCPY_CHK)
 	    {
-	      if (fcode == BUILT_IN_STPCPY_CHK)
-		{
-		  if (! ignore)
-		    return false;
-
-		  /* If return value of __stpcpy_chk is ignored,
-		     optimize into __strcpy_chk.  */
-		  fn = builtin_decl_explicit (BUILT_IN_STRCPY_CHK);
-		  if (!fn)
-		    return false;
-
-		  gimple *repl = gimple_build_call (fn, 3, dest, src, size);
-		  replace_call_with_call_and_fold (gsi, repl);
-		  return true;
-		}
-
-	      if (! len || TREE_SIDE_EFFECTS (len))
+	      if (! ignore)
 		return false;
 
-	      /* If c_strlen returned something, but not a constant,
-		 transform __strcpy_chk into __memcpy_chk.  */
-	      fn = builtin_decl_explicit (BUILT_IN_MEMCPY_CHK);
+	      /* If return value of __stpcpy_chk is ignored,
+		 optimize into __strcpy_chk.  */
+	      fn = builtin_decl_explicit (BUILT_IN_STRCPY_CHK);
 	      if (!fn)
 		return false;
 
-	      gimple_seq stmts = NULL;
-	      len = force_gimple_operand (len, &stmts, true, NULL_TREE);
-	      len = gimple_convert (&stmts, loc, size_type_node, len);
-	      len = gimple_build (&stmts, loc, PLUS_EXPR, size_type_node, len,
-				  build_int_cst (size_type_node, 1));
-	      gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
-	      gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
+	      gimple *repl = gimple_build_call (fn, 3, dest, src, size);
 	      replace_call_with_call_and_fold (gsi, repl);
 	      return true;
 	    }
-	}
-      else
-	maxlen = len;
 
-      if (! tree_int_cst_lt (maxlen, size))
-	return false;
+	  if (! len || TREE_SIDE_EFFECTS (len))
+	    return false;
+
+	  /* If c_strlen returned something, but not a constant,
+	     transform __strcpy_chk into __memcpy_chk.  */
+	  fn = builtin_decl_explicit (BUILT_IN_MEMCPY_CHK);
+	  if (!fn)
+	    return false;
+
+	  gimple_seq stmts = NULL;
+	  len = force_gimple_operand (len, &stmts, true, NULL_TREE);
+	  len = gimple_convert (&stmts, loc, size_type_node, len);
+	  len = gimple_build (&stmts, loc, PLUS_EXPR, size_type_node, len,
+			      build_int_cst (size_type_node, 1));
+	  gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
+	  gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
+	  replace_call_with_call_and_fold (gsi, repl);
+	  return true;
+	}
     }
 
   /* If __builtin_st{r,p}cpy_chk is used, assume st{r,p}cpy is available.  */
@@ -3222,26 +3212,10 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
 	 }
     }
 
-  if (! tree_fits_uhwi_p (size))
-    return false;
-
   tree maxlen = get_maxval_strlen (len, SRK_INT_VALUE);
-  if (! integer_all_onesp (size))
-    {
-      if (! tree_fits_uhwi_p (len))
-	{
-	  /* If LEN is not constant, try MAXLEN too.
-	     For MAXLEN only allow optimizing into non-_ocs function
-	     if SIZE is >= MAXLEN, never convert to __ocs_fail ().  */
-	  if (maxlen == NULL_TREE || ! tree_fits_uhwi_p (maxlen))
-	    return false;
-	}
-      else
-	maxlen = len;
-
-      if (tree_int_cst_lt (size, maxlen))
-	return false;
-    }
+  if (! integer_all_onesp (size)
+      && !known_safe (stmt, len, size) && !known_safe (stmt, maxlen, size))
+    return false;
 
   /* If __builtin_st{r,p}ncpy_chk is used, assume st{r,p}ncpy is available.  */
   fn = builtin_decl_explicit (fcode == BUILT_IN_STPNCPY_CHK
@@ -3359,27 +3333,11 @@ gimple_fold_builtin_snprintf_chk (gimple_stmt_iterator *gsi,
   size = gimple_call_arg (stmt, 3);
   fmt = gimple_call_arg (stmt, 4);
 
-  if (! tree_fits_uhwi_p (size))
+  tree maxlen = get_maxval_strlen (len, SRK_INT_VALUE);
+  if (! integer_all_onesp (size)
+      && !known_safe (stmt, len, size) && !known_safe (stmt, maxlen, size))
     return false;
 
-  if (! integer_all_onesp (size))
-    {
-      tree maxlen = get_maxval_strlen (len, SRK_INT_VALUE);
-      if (! tree_fits_uhwi_p (len))
-	{
-	  /* If LEN is not constant, try MAXLEN too.
-	     For MAXLEN only allow optimizing into non-_ocs function
-	     if SIZE is >= MAXLEN, never convert to __ocs_fail ().  */
-	  if (maxlen == NULL_TREE || ! tree_fits_uhwi_p (maxlen))
-	    return false;
-	}
-      else
-	maxlen = len;
-
-      if (tree_int_cst_lt (size, maxlen))
-	return false;
-    }
-
   if (!init_target_chars ())
     return false;
 
@@ -3438,9 +3396,6 @@ gimple_fold_builtin_sprintf_chk (gimple_stmt_iterator *gsi,
   size = gimple_call_arg (stmt, 2);
   fmt = gimple_call_arg (stmt, 3);
 
-  if (! tree_fits_uhwi_p (size))
-    return false;
-
   len = NULL_TREE;
 
   if (!init_target_chars ())
@@ -3454,7 +3409,7 @@ gimple_fold_builtin_sprintf_chk (gimple_stmt_iterator *gsi,
       if (strchr (fmt_str, target_percent) == 0)
 	{
 	  if (fcode != BUILT_IN_SPRINTF_CHK || nargs == 4)
-	    len = build_int_cstu (size_type_node, strlen (fmt_str));
+	    len = build_int_cstu (size_type_node, strlen (fmt_str) + 1);
 	}
       /* If the format is "%s" and first ... argument is a string literal,
 	 we know the size too.  */
@@ -3468,19 +3423,18 @@ gimple_fold_builtin_sprintf_chk (gimple_stmt_iterator *gsi,
 	      arg = gimple_call_arg (stmt, 4);
 	      if (POINTER_TYPE_P (TREE_TYPE (arg)))
 		{
-		  len = c_strlen (arg, 1);
 		  if (! len || ! tree_fits_uhwi_p (len))
 		    len = NULL_TREE;
+		  else
+		    len = fold_build2 (PLUS_EXPR, ssizetype, c_strlen (arg, 1),
+				       ssize_int (1));
 		}
 	    }
 	}
     }
 
-  if (! integer_all_onesp (size))
-    {
-      if (! len || ! tree_int_cst_lt (len, size))
-	return false;
-    }
+  if (! integer_all_onesp (size) && !known_safe (stmt, len, size))
+    return false;
 
   /* Only convert __{,v}sprintf_chk to {,v}sprintf if flag is 0
      or if format doesn't contain % chars or is "%s".  */
diff --git a/gcc/testsuite/gcc.dg/Wobjsize-1.c b/gcc/testsuite/gcc.dg/Wobjsize-1.c
index 2bd2f93897b..988b8bcbf35 100644
--- a/gcc/testsuite/gcc.dg/Wobjsize-1.c
+++ b/gcc/testsuite/gcc.dg/Wobjsize-1.c
@@ -7,11 +7,12 @@ char buf[6];
 
 int main(int argc, char **argv)
 {
-  strcpy (buf,"hello ");    /* { dg-warning "\\\[-Wstringop-overflow" } */
+  strcpy (buf,"hello ");
   return 0;
 }
 
-/* { dg-message "file included" "included" { target *-*-* } 0 }
+/* { dg-warning "\\\[-Wstringop-overflow" "warning" { target *-*-* } 0 }
+   { dg-message "file included" "included" { target *-*-* } 0 }
    { dg-message "inlined from" "inlined" { target *-*-* } 0 }
 
    The test might emit two warnings, one for the strcpy call and
diff --git a/gcc/testsuite/gcc.dg/builtin-chk-fold.c b/gcc/testsuite/gcc.dg/builtin-chk-fold.c
new file mode 100644
index 00000000000..517b146b50f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/builtin-chk-fold.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#define bos(__d) __builtin_object_size ((__d), 0)
+
+char *
+safe (const char *src, int cond, __SIZE_TYPE__ len)
+{
+  char *dst;
+
+  if (cond)
+    dst = __builtin_malloc (1024);
+  else
+    dst = __builtin_malloc (2048);
+
+  len = len > 2048 ? 2048 : len;
+
+  return __builtin___memcpy_chk (dst, src, len, bos (dst));
+}
+
+/* { dg-final { scan-assembler-not "__memcpy_chk" } } */
-- 
2.31.1



More information about the Gcc-patches mailing list