[PATCH 1/3] gimple-fold: Transform stp*cpy_chk to str*cpy directly

Siddhesh Poyarekar siddhesh@gotplt.org
Thu Nov 11 19:41:14 GMT 2021


Avoid going through another folding cycle and use the ignore flag to
directly transform BUILT_IN_STPCPY_CHK to BUILT_IN_STRCPY when set,
likewise for BUILT_IN_STPNCPY_CHK to BUILT_IN_STPNCPY.

Dump the transformation in dump_file so that we can verify in tests that
the direct transformation actually happened.

gcc/ChangeLog:

	* gimple-fold.c (gimple_fold_builtin_stxcpy_chk,
	gimple_fold_builtin_stxncpy_chk): Use BUILT_IN_STRNCPY if return
	value is not used.

gcc/testsuite/ChangeLog:

	* gcc.dg/fold-stringops.c: New test.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
---
 gcc/gimple-fold.c                       | 50 +++++++++++++++++--------
 gcc/testsuite/gcc.dg/fold-stringops-1.c | 23 ++++++++++++
 2 files changed, 57 insertions(+), 16 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/fold-stringops-1.c

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 6e25a7c05db..92e15784803 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -3088,6 +3088,19 @@ gimple_fold_builtin_memory_chk (gimple_stmt_iterator *gsi,
   return true;
 }
 
+static void
+dump_transformation (gimple *from, gimple *to)
+{
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "transformed ");
+      print_generic_expr (dump_file, gimple_call_fn (from), dump_flags);
+      fprintf (dump_file, " to ");
+      print_generic_expr (dump_file, gimple_call_fn (to), dump_flags);
+      fprintf (dump_file, "\n");
+    }
+}
+
 /* Fold a call to the __st[rp]cpy_chk builtin.
    DEST, SRC, and SIZE are the arguments to the call.
    IGNORE is true if return value can be ignored.  FCODE is the BUILT_IN_*
@@ -3184,12 +3197,13 @@ gimple_fold_builtin_stxcpy_chk (gimple_stmt_iterator *gsi,
     }
 
   /* If __builtin_st{r,p}cpy_chk is used, assume st{r,p}cpy is available.  */
-  fn = builtin_decl_explicit (fcode == BUILT_IN_STPCPY_CHK
+  fn = builtin_decl_explicit (fcode == BUILT_IN_STPCPY_CHK && !ignore
 			      ? BUILT_IN_STPCPY : BUILT_IN_STRCPY);
   if (!fn)
     return false;
 
   gimple *repl = gimple_build_call (fn, 2, dest, src);
+  dump_transformation (stmt, repl);
   replace_call_with_call_and_fold (gsi, repl);
   return true;
 }
@@ -3209,19 +3223,6 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
   bool ignore = gimple_call_lhs (stmt) == NULL_TREE;
   tree fn;
 
-  if (fcode == BUILT_IN_STPNCPY_CHK && ignore)
-    {
-       /* If return value of __stpncpy_chk is ignored,
-          optimize into __strncpy_chk.  */
-       fn = builtin_decl_explicit (BUILT_IN_STRNCPY_CHK);
-       if (fn)
-	 {
-	   gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
-	   replace_call_with_call_and_fold (gsi, repl);
-	   return true;
-	 }
-    }
-
   if (! tree_fits_uhwi_p (size))
     return false;
 
@@ -3234,7 +3235,23 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
 	     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;
+	    {
+	      if (fcode == BUILT_IN_STPNCPY_CHK && ignore)
+		{
+		  /* If return value of __stpncpy_chk is ignored,
+		     optimize into __strncpy_chk.  */
+		  fn = builtin_decl_explicit (BUILT_IN_STRNCPY_CHK);
+		  if (fn)
+		    {
+		      gimple *repl = gimple_build_call (fn, 4, dest, src, len,
+							size);
+		      replace_call_with_call_and_fold (gsi, repl);
+		      return true;
+		    }
+		}
+
+	      return false;
+	    }
 	}
       else
 	maxlen = len;
@@ -3244,12 +3261,13 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
     }
 
   /* 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
+  fn = builtin_decl_explicit (fcode == BUILT_IN_STPNCPY_CHK && !ignore
 			      ? BUILT_IN_STPNCPY : BUILT_IN_STRNCPY);
   if (!fn)
     return false;
 
   gimple *repl = gimple_build_call (fn, 3, dest, src, len);
+  dump_transformation (stmt, repl);
   replace_call_with_call_and_fold (gsi, repl);
   return true;
 }
diff --git a/gcc/testsuite/gcc.dg/fold-stringops-1.c b/gcc/testsuite/gcc.dg/fold-stringops-1.c
new file mode 100644
index 00000000000..712dd369e7c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-stringops-1.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-lower-details" } */
+
+char dst[2048];
+
+char *
+copy1 (const char *src, int cond)
+{
+  __builtin___stpncpy_chk (dst, src, 42, __builtin_object_size (dst, 0));
+
+  return dst;
+}
+
+char *
+copy2 (void)
+{
+  __builtin___stpcpy_chk (dst, "Hello world", __builtin_object_size (dst, 0));
+
+  return dst;
+}
+/* { dg-final { scan-tree-dump "transformed __builtin___stpncpy_chk to __builtin_strncpy" "lower" } } */
+/* { dg-final { scan-tree-dump "transformed __builtin___stpcpy_chk to __builtin_strcpy" "lower" } } */
+
-- 
2.31.1



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