[PATCH] Fix bitmap_bit_in_range_p (PR tree-optimization/82493).

[Martin Liška <mliska at suse dot cz>]

Hi.

This fixes some implementations mistakes in sbitmap.c (bitmap_bit_in_range_p). There's reference
to implementation one can take inspiration from:
https://www.cs.umd.edu/class/sum2003/cmsc311/Notes/BitOp/bitRange.html

Problem with our implementation is that one can't do:
(SBITMAP_ELT_TYPE)1 << SBITMAP_ELT_BITS (that would overflow)
Thus I do conditionally ~(SBITMAP_ELT_TYPE)0 at some places in the code.

I also added quite some unit tests for the method. But another questions pop up:
1) there are missing boundary asserts (or checking asserts) in sbitmap.c
2) we should probably include test-cases also for other functions

I can work on that (probably later) if desired?

And my patch breaks ssa-dse-26.c test-case, because now it properly returns true for:

#0  bitmap_bit_in_range_p (bmap=0x21c4940, start=0, end=8) at ../../gcc/sbitmap.c:326
#1  0x0000000000d618f5 in live_bytes_read (use_ref=..., ref=0x7fffffffd480, live=0x21c4940) at ../../gcc/tree-ssa-dse.c:496
#2  0x0000000000d61c4d in dse_classify_store (ref=0x7fffffffd480, stmt=0x155553ea7d70, use_stmt=0x7fffffffd470, byte_tracking_enabled=true, live_bytes=0x21c4940) at ../../gcc/tree-ssa-dse.c:594
#3  0x0000000000d6235b in dse_dom_walker::dse_optimize_stmt (this=0x7fffffffd5c0, gsi=0x7fffffffd530) at ../../gcc/tree-ssa-dse.c:820
#4  0x0000000000d62461 in dse_dom_walker::before_dom_children (this=0x7fffffffd5c0, bb=0x155553d76270) at ../../gcc/tree-ssa-dse.c:852
#5  0x00000000013b1698 in dom_walker::walk (this=0x7fffffffd5c0, bb=0x155553d76270) at ../../gcc/domwalk.c:308
#6  0x0000000000d625ac in (anonymous namespace)::pass_dse::execute (this=0x21d58c0, fun=0x155553eac0b0) at ../../gcc/tree-ssa-dse.c:906
#7  0x0000000000b27441 in execute_one_pass (pass=pass@entry=0x21d58c0) at ../../gcc/passes.c:2495
#8  0x0000000000b27d01 in execute_pass_list_1 (pass=0x21d58c0) at ../../gcc/passes.c:2584
#9  0x0000000000b27d13 in execute_pass_list_1 (pass=0x21d5480) at ../../gcc/passes.c:2585
#10 0x0000000000b27d55 in execute_pass_list (fn=<optimized out>, pass=<optimized out>) at ../../gcc/passes.c:2595
#11 0x0000000000b26681 in do_per_function_toporder (callback=callback@entry=0xb27d40 <execute_pass_list(function*, opt_pass*)>, data=0x21d5300) at ../../gcc/passes.c:1737
#12 0x0000000000b283d7 in execute_ipa_pass_list (pass=0x21d52a0) at ../../gcc/passes.c:2935
#13 0x00000000007d29d2 in ipa_passes () at ../../gcc/cgraphunit.c:2399
#14 symbol_table::compile (this=this@entry=0x155553d6e100) at ../../gcc/cgraphunit.c:2534
#15 0x00000000007d5277 in symbol_table::compile (this=0x155553d6e100) at ../../gcc/cgraphunit.c:2695
#16 symbol_table::finalize_compilation_unit (this=0x155553d6e100) at ../../gcc/cgraphunit.c:2692
#17 0x0000000000c118ac in compile_file () at ../../gcc/toplev.c:481
#18 0x0000000000c13eee in do_compile () at ../../gcc/toplev.c:2037
#19 0x0000000000c141da in toplev::main (this=0x7fffffffd85e, argc=21, argv=0x7fffffffd958) at ../../gcc/toplev.c:2172
#20 0x000000000061aeab in main (argc=21, argv=0x7fffffffd958) at ../../gcc/main.c:39

(gdb) p debug(bmap)
n_bits = 256, set = {8 9 10 11 12 13 14 15 }

Jeff can you please help me?
Apart from that the patch can bootstrap on ppc64le-redhat-linux and survives regression tests.

Ready to be installed?
Martin

Thanks,
Martin

gcc/ChangeLog:

2017-10-10  Martin Liska  <mliska@suse.cz>

	PR tree-optimization/82493
	* sbitmap.c (bitmap_bit_in_range_p): Fix the implementation.
	(test_range_functions): New function.
	(sbitmap_c_tests): Likewise.
	* selftest-run-tests.c (selftest::run_tests): Run new tests.
	* selftest.h (sbitmap_c_tests): New function.
---
 gcc/sbitmap.c            | 118 ++++++++++++++++++++++++++++++++++++++++-------
 gcc/selftest-run-tests.c |   1 +
 gcc/selftest.h           |   1 +
 3 files changed, 103 insertions(+), 17 deletions(-)


diff --git a/gcc/sbitmap.c b/gcc/sbitmap.c
index 4bf13a11a1d..baef4d05f0d 100644
--- a/gcc/sbitmap.c
+++ b/gcc/sbitmap.c
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "sbitmap.h"
+#include "selftest.h"
 
 typedef SBITMAP_ELT_TYPE *sbitmap_ptr;
 typedef const SBITMAP_ELT_TYPE *const_sbitmap_ptr;
@@ -322,29 +323,22 @@ bitmap_set_range (sbitmap bmap, unsigned int start, unsigned int count)
 bool
 bitmap_bit_in_range_p (const_sbitmap bmap, unsigned int start, unsigned int end)
 {
+  gcc_checking_assert (start <= end);
   unsigned int start_word = start / SBITMAP_ELT_BITS;
   unsigned int start_bitno = start % SBITMAP_ELT_BITS;
 
-  /* Testing within a word, starting at the beginning of a word.  */
-  if (start_bitno == 0 && (end - start) < SBITMAP_ELT_BITS)
-    {
-      SBITMAP_ELT_TYPE mask = ((SBITMAP_ELT_TYPE)1 << (end - start)) - 1;
-      return (bmap->elms[start_word] & mask) != 0;
-    }
-
   unsigned int end_word = end / SBITMAP_ELT_BITS;
   unsigned int end_bitno = end % SBITMAP_ELT_BITS;
 
-  /* Testing starts somewhere in the middle of a word.  Test up to the
-     end of the word or the end of the requested region, whichever comes
-     first.  */
+  /* Check beginning of first word if different from zero.  */
   if (start_bitno != 0)
     {
-      unsigned int nbits = ((start_word == end_word)
-			    ? end_bitno - start_bitno
-			    : SBITMAP_ELT_BITS - start_bitno);
-      SBITMAP_ELT_TYPE mask = ((SBITMAP_ELT_TYPE)1 << nbits) - 1;
-      mask <<= start_bitno;
+      SBITMAP_ELT_TYPE high_mask = ~(SBITMAP_ELT_TYPE)0;
+      if (start_word == end_word && end_bitno + 1 < SBITMAP_ELT_BITS)
+	high_mask = ((SBITMAP_ELT_TYPE)1 << (end_bitno + 1)) - 1;
+
+      SBITMAP_ELT_TYPE low_mask = ((SBITMAP_ELT_TYPE)1 << start_bitno) - 1;
+      SBITMAP_ELT_TYPE mask = high_mask - low_mask;
       if (bmap->elms[start_word] & mask)
 	return true;
       start_word++;
@@ -364,8 +358,9 @@ bitmap_bit_in_range_p (const_sbitmap bmap, unsigned int start, unsigned int end)
     }
 
   /* Now handle residuals in the last word.  */
-  SBITMAP_ELT_TYPE mask
-    = ((SBITMAP_ELT_TYPE)1 << (SBITMAP_ELT_BITS - end_bitno)) - 1;
+  SBITMAP_ELT_TYPE mask = ~(SBITMAP_ELT_TYPE)0;
+  if (end_bitno + 1 < SBITMAP_ELT_BITS)
+    mask = ((SBITMAP_ELT_TYPE)1 << (end_bitno + 1)) - 1;
   return (bmap->elms[start_word] & mask) != 0;
 }
 
@@ -821,3 +816,92 @@ dump_bitmap_vector (FILE *file, const char *title, const char *subtitle,
 
   fprintf (file, "\n");
 }
+
+#if CHECKING_P
+
+namespace selftest {
+
+/* Selftests for sbitmaps.  */
+
+
+/* Verify range functions for sbitmap.  */
+
+static void
+test_range_functions ()
+{
+  sbitmap s = sbitmap_alloc (1024);
+  bitmap_clear (s);
+
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 512, 1023));
+  bitmap_set_bit (s, 100);
+
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 512, 1023));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 99));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 101, 1023));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 1, 100));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 64, 100));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 100, 100));
+  ASSERT_TRUE (bitmap_bit_p (s, 100));
+
+  s = sbitmap_alloc (64);
+  bitmap_clear (s);
+  bitmap_set_bit (s, 63);
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 63));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 1, 63));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 63, 63));
+  ASSERT_TRUE (bitmap_bit_p (s, 63));
+
+  s = sbitmap_alloc (1024);
+  bitmap_clear (s);
+  bitmap_set_bit (s, 128);
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 127));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 129, 1023));
+
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 128));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 1, 128));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 128, 255));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 128, 254));
+  ASSERT_TRUE (bitmap_bit_p (s, 128));
+
+  bitmap_clear (s);
+  bitmap_set_bit (s, 8);
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 8));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 12));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 63));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 127));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 512));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 8, 8));
+  ASSERT_TRUE (bitmap_bit_p (s, 8));
+
+  bitmap_clear (s);
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 0));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 8));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 63));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 1, 63));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 0, 256));
+
+  bitmap_set_bit (s, 0);
+  bitmap_set_bit (s, 16);
+  bitmap_set_bit (s, 32);
+  bitmap_set_bit (s, 48);
+  bitmap_set_bit (s, 64);
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 0, 0));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 1, 16));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 48, 63));
+  ASSERT_TRUE (bitmap_bit_in_range_p (s, 64, 64));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 1, 15));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 17, 31));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 49, 63));
+  ASSERT_FALSE (bitmap_bit_in_range_p (s, 65, 1023));
+}
+
+/* Run all of the selftests within this file.  */
+
+void
+sbitmap_c_tests ()
+{
+  test_range_functions ();
+}
+
+} // namespace selftest
+#endif /* CHECKING_P */
diff --git a/gcc/selftest-run-tests.c b/gcc/selftest-run-tests.c
index 30e476d14c5..5c84f3a0737 100644
--- a/gcc/selftest-run-tests.c
+++ b/gcc/selftest-run-tests.c
@@ -56,6 +56,7 @@ selftest::run_tests ()
 
   /* Low-level data structures.  */
   bitmap_c_tests ();
+  sbitmap_c_tests ();
   et_forest_c_tests ();
   hash_map_tests_c_tests ();
   hash_set_tests_c_tests ();
diff --git a/gcc/selftest.h b/gcc/selftest.h
index 0572fefd281..2e649a70b9e 100644
--- a/gcc/selftest.h
+++ b/gcc/selftest.h
@@ -171,6 +171,7 @@ extern const char *path_to_selftest_files;
 /* Declarations for specific families of tests (by source file), in
    alphabetical order.  */
 extern void bitmap_c_tests ();
+extern void sbitmap_c_tests ();
 extern void diagnostic_c_tests ();
 extern void diagnostic_show_locus_c_tests ();
 extern void edit_context_c_tests ();