re PR tree-optimization/87314 (pointless comparison of malloc result to a string not eliminated)

2019-05-03  Richard Biener  <rguenther@suse.de>

	PR middle-end/87314
	* match.pd (cmp (convert1?@2 addr@0) (convert2? addr@1)):
	Handle STRING_CST vs DECL or STRING_CST.

	* gcc.dg/pr87314-1.c: New testcase.

From-SVN: r270845

gcc/ChangeLog

 2019-05-03  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/87314
+	* match.pd (cmp (convert1?@2 addr@0) (convert2? addr@1)):
+	Handle STRING_CST vs DECL or STRING_CST.
+
+2019-05-03  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88963
 	* tree-ssa-forwprop.c (pass_forwprop::execute): Rewrite
 	vector loads feeding only BIT_FIELD_REFs to component

gcc/match.pd

@@ -3905,7 +3905,24 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
          equal = (base0 == base1);
        if (equal == 0)
 	 {
-	   if (!DECL_P (base0) || !DECL_P (base1))
+	   HOST_WIDE_INT ioff0 = -1, ioff1 = -1;
+	   off0.is_constant (&ioff0);
+	   off1.is_constant (&ioff1);
+	   if ((DECL_P (base0) && TREE_CODE (base1) == STRING_CST)
+	       || (TREE_CODE (base0) == STRING_CST && DECL_P (base1))
+	       || (TREE_CODE (base0) == STRING_CST
+		   && TREE_CODE (base1) == STRING_CST
+		   && ioff0 >= 0 && ioff1 >= 0
+		   && ioff0 < TREE_STRING_LENGTH (base0)
+		   && ioff1 < TREE_STRING_LENGTH (base1)
+		   /* This is a too conservative test that the STRING_CSTs
+		      will not end up being string-merged.  */
+		   && strncmp (TREE_STRING_POINTER (base0) + ioff0,
+			       TREE_STRING_POINTER (base1) + ioff1,
+			       MIN (TREE_STRING_LENGTH (base0) - ioff0,
+				    TREE_STRING_LENGTH (base1) - ioff1)) != 0))
+	     ;
+	   else if (!DECL_P (base0) || !DECL_P (base1))
 	     equal = 2;
 	   else if (cmp != EQ_EXPR && cmp != NE_EXPR)
 	     equal = 2;

gcc/testsuite/ChangeLog

 2019-05-03  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/87314
+	* gcc.dg/pr87314-1.c: New testcase.
+
+2019-05-03  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88963
 	* gcc.dg/tree-ssa/ssa-fre-31.c: Disable forwprop.
 	* gcc.target/i386/pr88963-1.c: New testcase.

gcc/testsuite/gcc.dg/pr87314-1.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+int f(){ int a; return &a==(void *)"hello"; }
+int g(){ return "bye"=="hello"; }
+int h() { return "bye"=="hellobye"+5; }
+
+/* { dg-final { scan-tree-dump-times "hello" 1 "original" } } */
+/* The test in h() should be retained because the result depends on
+   string merging.  */
+/* { dg-final { scan-assembler "hello" } } */