PR 69400: Invalid 128-bit modulus result

As described in the PR, wi::divmod_internal was sign- rather than
zero-extending a modulus result in cases where the result has fewer
HWIs than the precision and the upper bit of the upper HWI was set.

This patch tries to make things more robust by getting wi_pack
to handle the canonicalisation step itself.

Tested on x86_64-linux-gnu.  I added tests to the wide-int
plugin since that seemed more direct.

gcc/
	PR tree-optimization/69400
	* wide-int.cc (wi_pack): Take the precision as argument and
	perform canonicalization here rather than in the callers.
	Use the main loop to handle all full-width HWIs.  Add a
	zero HWI if in_len isn't a full result.
	(wi::divmod_internal): Update accordingly.
	(wi::mul_internal): Likewise.  Simplify.

gcc/testsuite/
	PR tree-optimization/69400
	* gcc.dg/plugin/wide-int_plugin.c (test_wide_int_mod_trunc): New
	function.
	(plugin_init): Call it.
	* gcc.dg/torture/pr69400.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@232817 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 90 insertions, 30 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9f124dcb59f..7a4e57bddbd 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2016-01-26  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR tree-optimization/69400
+	* wide-int.cc (wi_pack): Take the precision as argument and
+	perform canonicalization here rather than in the callers.
+	Use the main loop to handle all full-width HWIs.  Add a
+	zero HWI if in_len isn't a full result.
+	(wi::divmod_internal): Update accordingly.
+	(wi::mul_internal): Likewise.  Simplify.
+
 2016-01-25  Aditya Kumar  <aditya.k7@samsung.com>
 	    Sebastian Pop  <s.pop@samsung.com>
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5c5d28a951f..ffb4314b9e6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2016-01-26  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR tree-optimization/69400
+	* gcc.dg/plugin/wide-int_plugin.c (test_wide_int_mod_trunc): New
+	function.
+	(plugin_init): Call it.
+	* gcc.dg/torture/pr69400.c: New test.
+
 2016-01-26  Christophe Lyon  <christophe.lyon@linaro.org>
 
 	* gcc.target/arm/pr68674.c: Check and use arm_fp effective target.
diff --git a/gcc/testsuite/gcc.dg/plugin/wide-int_plugin.c b/gcc/testsuite/gcc.dg/plugin/wide-int_plugin.c
index 17604c8cf99..eea56be5e7c 100644
--- a/gcc/testsuite/gcc.dg/plugin/wide-int_plugin.c
+++ b/gcc/testsuite/gcc.dg/plugin/wide-int_plugin.c
@@ -36,11 +36,44 @@ test_wide_int_round_sdiv (void)
     abort ();
 }
 
+static void
+test_wide_int_mod_trunc (void)
+{
+  for (unsigned int i = 1; i < MAX_BITSIZE_MODE_ANY_INT; ++i)
+    {
+      if (wi::smod_trunc (wi::lshift (1, i + 1) - 3,
+			  wi::lshift (1, i) - 1)
+	  != wi::lshift (1, i) - 2)
+	abort ();
+      for (unsigned int base = 32; base <= MAX_BITSIZE_MODE_ANY_INT; base *= 2)
+	for (int bias = -1; bias <= 1; ++bias)
+	  {
+	    unsigned int precision = base + bias;
+	    if (i + 1 < precision && precision <= MAX_BITSIZE_MODE_ANY_INT)
+	      {
+		wide_int one = wi::uhwi (1, precision);
+		wide_int a = wi::lshift (one, i + 1) - 3;
+		wide_int b = wi::lshift (one, i) - 1;
+		wide_int c = wi::lshift (one, i) - 2;
+		if (wi::umod_trunc (a, b) != c)
+		  abort ();
+		if (wi::smod_trunc (a, b) != c)
+		  abort ();
+		if (wi::smod_trunc (-a, b) != -c)
+		  abort ();
+		if (wi::smod_trunc (a, -b) != c)
+		  abort ();
+	      }
+	  }
+    }
+}
+
 int
 plugin_init (struct plugin_name_args *plugin_info,
 	     struct plugin_gcc_version *version)
 {
   test_double_int_round_udiv ();
   test_wide_int_round_sdiv ();
+  test_wide_int_mod_trunc ();
   return 0;
 }
diff --git a/gcc/testsuite/gcc.dg/torture/pr69400.c b/gcc/testsuite/gcc.dg/torture/pr69400.c
new file mode 100644
index 00000000000..e0eb521244d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr69400.c
@@ -0,0 +1,20 @@
+/* { dg-do run { target int128 } } */
+
+typedef unsigned __int128 u128;
+
+u128 __attribute__((noinline, noclone))
+foo(void)
+{
+	u128 u = -2;
+	u %= 0xffffffffffffffffllu;
+	return u;
+}
+
+int
+main()
+{
+	u128 x = foo();
+	if (x != 0xfffffffffffffffellu)
+		__builtin_abort();
+	return 0;
+}
diff --git a/gcc/wide-int.cc b/gcc/wide-int.cc
index 35eee2c3bc9..195ac26fa56 100644
--- a/gcc/wide-int.cc
+++ b/gcc/wide-int.cc
@@ -1214,30 +1214,32 @@ wi_unpack (unsigned HOST_HALF_WIDE_INT *result, const HOST_WIDE_INT *input,
     result[j++] = mask;
 }
 
-/* The inverse of wi_unpack.  IN_LEN is the the number of input
-   blocks.  The number of output blocks will be half this amount.  */
-static void
-wi_pack (unsigned HOST_WIDE_INT *result,
+/* The inverse of wi_unpack.  IN_LEN is the number of input
+   blocks and PRECISION is the precision of the result.  Return the
+   number of blocks in the canonicalized result.  */
+static unsigned int
+wi_pack (HOST_WIDE_INT *result,
 	 const unsigned HOST_HALF_WIDE_INT *input,
-	 unsigned int in_len)
+	 unsigned int in_len, unsigned int precision)
 {
   unsigned int i = 0;
   unsigned int j = 0;
+  unsigned int blocks_needed = BLOCKS_NEEDED (precision);
 
-  while (i + 2 < in_len)
+  while (i + 1 < in_len)
     {
-      result[j++] = (unsigned HOST_WIDE_INT)input[i]
-	| ((unsigned HOST_WIDE_INT)input[i + 1]
-	   << HOST_BITS_PER_HALF_WIDE_INT);
+      result[j++] = ((unsigned HOST_WIDE_INT) input[i]
+		     | ((unsigned HOST_WIDE_INT) input[i + 1]
+			<< HOST_BITS_PER_HALF_WIDE_INT));
       i += 2;
     }
 
   /* Handle the case where in_len is odd.   For this we zero extend.  */
   if (in_len & 1)
-    result[j++] = (unsigned HOST_WIDE_INT)input[i];
-  else
-    result[j++] = (unsigned HOST_WIDE_INT)input[i]
-      | ((unsigned HOST_WIDE_INT)input[i + 1] << HOST_BITS_PER_HALF_WIDE_INT);
+    result[j++] = (unsigned HOST_WIDE_INT) input[i];
+  else if (j < blocks_needed)
+    result[j++] = 0;
+  return canonize (result, j, precision);
 }
 
 /* Multiply Op1 by Op2.  If HIGH is set, only the upper half of the
@@ -1460,19 +1462,8 @@ wi::mul_internal (HOST_WIDE_INT *val, const HOST_WIDE_INT *op1val,
 	  *overflow = true;
     }
 
-  if (high)
-    {
-      /* compute [prec] <- ([prec] * [prec]) >> [prec] */
-      wi_pack ((unsigned HOST_WIDE_INT *) val,
-	       &r[half_blocks_needed], half_blocks_needed);
-      return canonize (val, blocks_needed, prec);
-    }
-  else
-    {
-      /* compute [prec] <- ([prec] * [prec]) && ((1 << [prec]) - 1) */
-      wi_pack ((unsigned HOST_WIDE_INT *) val, r, half_blocks_needed);
-      return canonize (val, blocks_needed, prec);
-    }
+  int r_offset = high ? half_blocks_needed : 0;
+  return wi_pack (val, &r[r_offset], half_blocks_needed, prec);
 }
 
 /* Compute the population count of X.  */
@@ -1847,8 +1838,7 @@ wi::divmod_internal (HOST_WIDE_INT *quotient, unsigned int *remainder_len,
   unsigned int quotient_len = 0;
   if (quotient)
     {
-      wi_pack ((unsigned HOST_WIDE_INT *) quotient, b_quotient, m);
-      quotient_len = canonize (quotient, (m + 1) / 2, dividend_prec);
+      quotient_len = wi_pack (quotient, b_quotient, m, dividend_prec);
       /* The quotient is neg if exactly one of the divisor or dividend is
 	 neg.  */
       if (dividend_neg != divisor_neg)
@@ -1859,8 +1849,7 @@ wi::divmod_internal (HOST_WIDE_INT *quotient, unsigned int *remainder_len,
 
   if (remainder)
     {
-      wi_pack ((unsigned HOST_WIDE_INT *) remainder, b_remainder, n);
-      *remainder_len = canonize (remainder, (n + 1) / 2, dividend_prec);
+      *remainder_len = wi_pack (remainder, b_remainder, n, dividend_prec);
       /* The remainder is always the same sign as the dividend.  */
       if (dividend_neg)
 	*remainder_len = wi::sub_large (remainder, zeros, 1, remainder,