Patchwork some integer undefined behaviors in gcc

login
register
mail settings
Submitter Richard Henderson
Date Aug. 5, 2010, 7:46 p.m.
Message ID <4C5B1507.2090603@redhat.com>
Download mbox | patch
Permalink /patch/61017/
State New
Headers show

Comments

Richard Henderson - Aug. 5, 2010, 7:46 p.m.
On 08/03/2010 04:27 PM, John Regehr wrote:
> <../../gcc/builtins.c, (7681:57)> : Op: -, Reason : Signed Subtraction Overflow, UNARY OPERATION: right (int32): -2147483648 
> <../../gcc/builtins.c, (7699:57)> : Op: -, Reason : Signed Subtraction Overflow, UNARY OPERATION: right (int32): -2147483648 

These were due to an (X & -X) idiom.  One could fix it by making sure that X
is (cast to) unsigned, but we can avoid those two operations altogether if
we simply use CTZ directly.

Tested on x86_64-linux.  Committed.


r~
* toplev.h (ctz_hwi, clz_hwi, ffs_hwi): New.
	(floor_log2): Use clz_hwi.
	(exact_log2): Use ctz_hwi.
	* toplev.c (ctz_hwi, clz_hwi, ffs_hwi): New.
	* builtins.c (fold_builtin_bitop): Use them.
	* simplify-rtx.c (simplify_const_unary_operation): Likewise.
	* combine.c (get_pos_from_mask): Use ctz_hwi.
	* double-int.c (double_int_ctz): Likewise.
	* explow.c (force_reg): Likewise.
	* tree.h (SET_DECL_OFFSET_ALIGN): Use ffs_hwi.

Patch

diff --git a/gcc/builtins.c b/gcc/builtins.c
index b20426c..096fec6 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -7676,9 +7676,9 @@  fold_builtin_bitop (tree fndecl, tree arg)
 	{
 	CASE_INT_FN (BUILT_IN_FFS):
 	  if (lo != 0)
-	    result = exact_log2 (lo & -lo) + 1;
+	    result = ffs_hwi (lo);
 	  else if (hi != 0)
-	    result = HOST_BITS_PER_WIDE_INT + exact_log2 (hi & -hi) + 1;
+	    result = HOST_BITS_PER_WIDE_INT + ffs_hwi (hi);
 	  else
 	    result = 0;
 	  break;
@@ -7694,9 +7694,9 @@  fold_builtin_bitop (tree fndecl, tree arg)
 
 	CASE_INT_FN (BUILT_IN_CTZ):
 	  if (lo != 0)
-	    result = exact_log2 (lo & -lo);
+	    result = ctz_hwi (lo);
 	  else if (hi != 0)
-	    result = HOST_BITS_PER_WIDE_INT + exact_log2 (hi & -hi);
+	    result = HOST_BITS_PER_WIDE_INT + ctz_hwi (hi);
 	  else if (! CTZ_DEFINED_VALUE_AT_ZERO (TYPE_MODE (type), result))
 	    result = width;
 	  break;
@@ -7706,7 +7706,7 @@  fold_builtin_bitop (tree fndecl, tree arg)
 	  while (lo)
 	    result++, lo &= lo - 1;
 	  while (hi)
-	    result++, hi &= hi - 1;
+	    result++, hi &= (unsigned HOST_WIDE_INT) hi - 1;
 	  break;
 
 	CASE_INT_FN (BUILT_IN_PARITY):
@@ -7714,7 +7714,7 @@  fold_builtin_bitop (tree fndecl, tree arg)
 	  while (lo)
 	    result++, lo &= lo - 1;
 	  while (hi)
-	    result++, hi &= hi - 1;
+	    result++, hi &= (unsigned HOST_WIDE_INT) hi - 1;
 	  result &= 1;
 	  break;
 
diff --git a/gcc/combine.c b/gcc/combine.c
index 0725c86..41a0ec1 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7436,7 +7436,7 @@  static int
 get_pos_from_mask (unsigned HOST_WIDE_INT m, unsigned HOST_WIDE_INT *plen)
 {
   /* Get the bit number of the first 1 bit from the right, -1 if none.  */
-  int pos = exact_log2 (m & -m);
+  int pos = m ? ctz_hwi (m) : -1;
   int len = 0;
 
   if (pos >= 0)
diff --git a/gcc/double-int.c b/gcc/double-int.c
index 29e720b..cb63f85 100644
--- a/gcc/double-int.c
+++ b/gcc/double-int.c
@@ -859,15 +859,7 @@  double_int_ctz (double_int a)
   unsigned bits = a.low ? 0 : HOST_BITS_PER_WIDE_INT;
   if (!w)
     return HOST_BITS_PER_DOUBLE_INT;
-#if (GCC_VERSION >= 3004)
-  bits += CTZ_HWI (w);
-#else
-  while (!(w & 1))
-    {
-      w >>= 1;
-      bits += 1;
-    }
-#endif
+  bits += ctz_hwi (w);
   return bits;
 }
 
diff --git a/gcc/explow.c b/gcc/explow.c
index 09f786a..6f60b2e 100644
--- a/gcc/explow.c
+++ b/gcc/explow.c
@@ -707,9 +707,13 @@  force_reg (enum machine_mode mode, rtx x)
 	if (SYMBOL_REF_DECL (s) && DECL_P (SYMBOL_REF_DECL (s)))
 	  sa = DECL_ALIGN (SYMBOL_REF_DECL (s));
 
-	ca = exact_log2 (INTVAL (c) & -INTVAL (c)) * BITS_PER_UNIT;
-
-	align = MIN (sa, ca);
+	if (INTVAL (c) == 0)
+	  align = sa;
+	else
+	  {
+	    ca = ctz_hwi (INTVAL (c)) * BITS_PER_UNIT;
+	    align = MIN (sa, ca);
+	  }
       }
 
     if (align || (MEM_P (x) && MEM_POINTER (x)))
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 86de77e..a7a91e5 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -1197,10 +1197,8 @@  simplify_const_unary_operation (enum rtx_code code, enum machine_mode mode,
 	  break;
 
 	case FFS:
-	  /* Don't use ffs here.  Instead, get low order bit and then its
-	     number.  If arg0 is zero, this will return 0, as desired.  */
 	  arg0 &= GET_MODE_MASK (mode);
-	  val = exact_log2 (arg0 & (- arg0)) + 1;
+	  val = ffs_hwi (arg0);
 	  break;
 
 	case CLZ:
@@ -1221,7 +1219,7 @@  simplify_const_unary_operation (enum rtx_code code, enum machine_mode mode,
 		val = GET_MODE_BITSIZE (mode);
 	    }
 	  else
-	    val = exact_log2 (arg0 & -arg0);
+	    val = ctz_hwi (arg0);
 	  break;
 
 	case POPCOUNT:
@@ -1351,15 +1349,12 @@  simplify_const_unary_operation (enum rtx_code code, enum machine_mode mode,
 
 	case FFS:
 	  hv = 0;
-	  if (l1 == 0)
-	    {
-	      if (h1 == 0)
-		lv = 0;
-	      else
-		lv = HOST_BITS_PER_WIDE_INT + exact_log2 (h1 & -h1) + 1;
-	    }
+	  if (l1 != 0)
+	    lv = ffs_hwi (l1);
+	  else if (h1 != 0)
+	    lv = HOST_BITS_PER_WIDE_INT + ffs_hwi (h1);
 	  else
-	    lv = exact_log2 (l1 & -l1) + 1;
+	    lv = 0;
 	  break;
 
 	case CLZ:
@@ -1376,9 +1371,9 @@  simplify_const_unary_operation (enum rtx_code code, enum machine_mode mode,
 	case CTZ:
 	  hv = 0;
 	  if (l1 != 0)
-	    lv = exact_log2 (l1 & -l1);
+	    lv = ctz_hwi (l1);
 	  else if (h1 != 0)
-	    lv = HOST_BITS_PER_WIDE_INT + exact_log2 (h1 & -h1);
+	    lv = HOST_BITS_PER_WIDE_INT + ctz_hwi (h1);
 	  else if (! CTZ_DEFINED_VALUE_AT_ZERO (mode, lv))
 	    lv = GET_MODE_BITSIZE (mode);
 	  break;
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 3836d0c..ff82466 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -484,9 +484,9 @@  set_random_seed (const char *val)
 
 #if GCC_VERSION < 3004
 
-/* The functions floor_log2 and exact_log2 are defined as inline
-   functions in toplev.h if GCC_VERSION >= 3004.  The definitions here
-   are used for older versions of gcc.  */
+/* The functions clz_hwi, ctz_hwi, ffs_hwi, floor_log2 and exact_log2
+   are defined as inline functions in toplev.h if GCC_VERSION >= 3004.
+   The definitions here are used for older versions of gcc.  */
 
 /* Given X, an unsigned number, return the largest int Y such that 2**Y <= X.
    If X is 0, return -1.  */
@@ -530,6 +530,32 @@  exact_log2 (unsigned HOST_WIDE_INT x)
   return floor_log2 (x);
 }
 
+/* Given X, an unsigned number, return the number of least significant bits
+   that are zero.  When X == 0, the result is the word size.  */
+
+int
+ctz_hwi (unsigned HOST_WIDE_INT x)
+{
+  return x ? floor_log2 (x & -x) : HOST_BITS_PER_WIDE_INT;
+}
+
+/* Similarly for most significant bits.  */
+
+int
+clz_hwi (unsigned HOST_WIDE_INT x)
+{
+  return HOST_BITS_PER_WIDE_INT - 1 - floor_log2(x);
+}
+
+/* Similar to ctz_hwi, except that the least significant bit is numbered
+   starting from 1, and X == 0 yields 0.  */
+
+int
+ffs_hwi (unsigned HOST_WIDE_INT x)
+{
+  return 1 + floor_log2 (x & -x);
+}
+
 #endif /* GCC_VERSION < 3004 */
 
 /* Handler for fatal signals, such as SIGSEGV.  These are transformed
diff --git a/gcc/toplev.h b/gcc/toplev.h
index 44920ed..6de27a0 100644
--- a/gcc/toplev.h
+++ b/gcc/toplev.h
@@ -111,6 +111,10 @@  extern bool fast_math_flags_struct_set_p (struct cl_optimization *);
 /* Inline versions of the above for speed.  */
 #if GCC_VERSION < 3004
 
+extern int clz_hwi (unsigned HOST_WIDE_INT x);
+extern int ctz_hwi (unsigned HOST_WIDE_INT x);
+extern int ffs_hwi (unsigned HOST_WIDE_INT x);
+
 /* Return log2, or -1 if not exact.  */
 extern int exact_log2                  (unsigned HOST_WIDE_INT);
 
@@ -119,27 +123,57 @@  extern int floor_log2                  (unsigned HOST_WIDE_INT);
 
 #else /* GCC_VERSION >= 3004 */
 
+/* For convenience, define 0 -> word_size.  */
+static inline int
+clz_hwi (unsigned HOST_WIDE_INT x)
+{
+  if (x == 0)
+    return HOST_BITS_PER_WIDE_INT;
+# if HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONG
+  return __builtin_clzl (x);
+# elif HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONGLONG
+  return __builtin_clzll (x);
+# else
+  return __builtin_clz (x);
+# endif
+}
+
+static inline int
+ctz_hwi (unsigned HOST_WIDE_INT x)
+{
+  if (x == 0)
+    return HOST_BITS_PER_WIDE_INT;
+# if HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONG
+  return __builtin_ctzl (x);
+# elif HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONGLONG
+  return __builtin_ctzll (x);
+# else
+  return __builtin_ctz (x);
+# endif
+}
+
+static inline int
+ffs_hwi (unsigned HOST_WIDE_INT x)
+{
 # if HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONG
-#  define CLZ_HWI __builtin_clzl
-#  define CTZ_HWI __builtin_ctzl
+  return __builtin_ffsl (x);
 # elif HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONGLONG
-#  define CLZ_HWI __builtin_clzll
-#  define CTZ_HWI __builtin_ctzll
+  return __builtin_ffsll (x);
 # else
-#  define CLZ_HWI __builtin_clz
-#  define CTZ_HWI __builtin_ctz
+  return __builtin_ffs (x);
 # endif
+}
 
 static inline int
 floor_log2 (unsigned HOST_WIDE_INT x)
 {
-  return x ? HOST_BITS_PER_WIDE_INT - 1 - (int) CLZ_HWI (x) : -1;
+  return HOST_BITS_PER_WIDE_INT - 1 - clz_hwi (x);
 }
 
 static inline int
 exact_log2 (unsigned HOST_WIDE_INT x)
 {
-  return x == (x & -x) && x ? (int) CTZ_HWI (x) : -1;
+  return x == (x & -x) && x ? ctz_hwi (x) : -1;
 }
 
 #endif /* GCC_VERSION >= 3004 */
diff --git a/gcc/tree.h b/gcc/tree.h
index af8345a..931155c 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -2850,9 +2850,7 @@  struct GTY(()) tree_decl_with_rtl {
 
 /* Specify that DECL_ALIGN(NODE) is a multiple of X.  */
 #define SET_DECL_OFFSET_ALIGN(NODE, X) \
-  (FIELD_DECL_CHECK (NODE)->decl_common.off_align = exact_log2 ((X) & -(X)))
-/* 1 if the alignment for this type was requested by "aligned" attribute,
-   0 if it is the default for this type.  */
+  (FIELD_DECL_CHECK (NODE)->decl_common.off_align = ffs_hwi (X) - 1)
 
 /* For FIELD_DECLS, DECL_FCONTEXT is the *first* baseclass in
    which this FIELD_DECL is defined.  This information is needed when