[Sema] Re-land: Diagnose tautological comparison with type's min/max values

The first attempt, rL315614 was reverted because one libcxx
test broke, and i did not know at the time how to deal with it.

Summary:
Currently, clang only diagnoses completely out-of-range comparisons (e.g. `char` and constant `300`),
and comparisons of unsigned and `0`. But gcc also does diagnose the comparisons with the
`std::numeric_limits<>::max()` / `std::numeric_limits<>::min()` so to speak

Finally Fixes https://bugs.llvm.org/show_bug.cgi?id=34147
Continuation of https://reviews.llvm.org/D37565

Reviewers: rjmccall, rsmith, aaron.ballman

Reviewed By: rsmith

Subscribers: rtrieu, jroelofs, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D38101

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315875 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 514 insertions, 0 deletions

diff --git a/test/Sema/tautological-constant-compare.c b/test/Sema/tautological-constant-compare.c
new file mode 100644
index 0000000000..b9ade2a2db
--- /dev/null
+++ b/test/Sema/tautological-constant-compare.c
@@ -0,0 +1,514 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -DTEST -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wno-tautological-constant-compare -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -DTEST -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wno-tautological-constant-compare -verify -x c++ %s
+
+int value(void);
+
+#define macro(val) val
+
+#ifdef __cplusplus
+template<typename T>
+void TFunc() {
+  // Make sure that we do warn for normal variables in template functions !
+  unsigned char c = value();
+#ifdef TEST
+  if (c > 255) // expected-warning {{comparison 'unsigned char' > 255 is always false}}
+      return;
+#else
+  if (c > 255)
+      return;
+#endif
+
+  if (c > macro(255))
+      return;
+
+  T v = value();
+  if (v > 255)
+      return;
+  if (v > 32767)
+      return;
+}
+#endif
+
+int main()
+{
+#ifdef __cplusplus
+  TFunc<unsigned char>();
+  TFunc<signed short>();
+#endif
+
+  short s = value();
+
+#ifdef TEST
+  if (s == 32767)
+      return 0;
+  if (s != 32767)
+      return 0;
+  if (s < 32767)
+      return 0;
+  if (s <= 32767) // expected-warning {{comparison 'short' <= 32767 is always true}}
+      return 0;
+  if (s > 32767) // expected-warning {{comparison 'short' > 32767 is always false}}
+      return 0;
+  if (s >= 32767)
+      return 0;
+
+  if (32767 == s)
+      return 0;
+  if (32767 != s)
+      return 0;
+  if (32767 < s) // expected-warning {{comparison 32767 < 'short' is always false}}
+      return 0;
+  if (32767 <= s)
+      return 0;
+  if (32767 > s)
+      return 0;
+  if (32767 >= s) // expected-warning {{comparison 32767 >= 'short' is always true}}
+      return 0;
+
+  // FIXME: assumes two's complement
+  if (s == -32768)
+      return 0;
+  if (s != -32768)
+      return 0;
+  if (s < -32768) // expected-warning {{comparison 'short' < -32768 is always false}}
+      return 0;
+  if (s <= -32768)
+      return 0;
+  if (s > -32768)
+      return 0;
+  if (s >= -32768) // expected-warning {{comparison 'short' >= -32768 is always true}}
+      return 0;
+
+  if (-32768 == s)
+      return 0;
+  if (-32768 != s)
+      return 0;
+  if (-32768 < s)
+      return 0;
+  if (-32768 <= s) // expected-warning {{comparison -32768 <= 'short' is always true}}
+      return 0;
+  if (-32768 > s) // expected-warning {{comparison -32768 > 'short' is always false}}
+      return 0;
+  if (-32768 >= s)
+      return 0;
+
+  if (s == 32767UL)
+      return 0;
+  if (s != 32767UL)
+      return 0;
+  if (s < 32767UL)
+      return 0;
+  if (s <= 32767UL) // expected-warning {{comparison 'short' <= 32767 is always true}}
+      return 0;
+  if (s > 32767UL) // expected-warning {{comparison 'short' > 32767 is always false}}
+      return 0;
+  if (s >= 32767UL)
+      return 0;
+
+  if (32767UL == s)
+      return 0;
+  if (32767UL != s)
+      return 0;
+  if (32767UL < s) // expected-warning {{comparison 32767 < 'short' is always false}}
+      return 0;
+  if (32767UL <= s)
+      return 0;
+  if (32767UL > s)
+      return 0;
+  if (32767UL >= s) // expected-warning {{comparison 32767 >= 'short' is always true}}
+      return 0;
+
+  // FIXME: assumes two's complement
+  if (s == -32768L)
+      return 0;
+  if (s != -32768L)
+      return 0;
+  if (s < -32768L) // expected-warning {{comparison 'short' < -32768 is always false}}
+      return 0;
+  if (s <= -32768L)
+      return 0;
+  if (s > -32768L)
+      return 0;
+  if (s >= -32768L) // expected-warning {{comparison 'short' >= -32768 is always true}}
+      return 0;
+
+  if (-32768L == s)
+      return 0;
+  if (-32768L != s)
+      return 0;
+  if (-32768L < s)
+      return 0;
+  if (-32768L <= s) // expected-warning {{comparison -32768 <= 'short' is always true}}
+      return 0;
+  if (-32768L > s) // expected-warning {{comparison -32768 > 'short' is always false}}
+      return 0;
+  if (-32768L >= s)
+      return 0;
+#else
+  // expected-no-diagnostics
+  if (s == 32767)
+    return 0;
+  if (s != 32767)
+    return 0;
+  if (s < 32767)
+    return 0;
+  if (s <= 32767)
+    return 0;
+  if (s > 32767)
+    return 0;
+  if (s >= 32767)
+    return 0;
+
+  if (32767 == s)
+    return 0;
+  if (32767 != s)
+    return 0;
+  if (32767 < s)
+    return 0;
+  if (32767 <= s)
+    return 0;
+  if (32767 > s)
+    return 0;
+  if (32767 >= s)
+    return 0;
+
+  // FIXME: assumes two's complement
+  if (s == -32768)
+    return 0;
+  if (s != -32768)
+    return 0;
+  if (s < -32768)
+    return 0;
+  if (s <= -32768)
+    return 0;
+  if (s > -32768)
+    return 0;
+  if (s >= -32768)
+    return 0;
+
+  if (-32768 == s)
+    return 0;
+  if (-32768 != s)
+    return 0;
+  if (-32768 < s)
+    return 0;
+  if (-32768 <= s)
+    return 0;
+  if (-32768 > s)
+    return 0;
+  if (-32768 >= s)
+    return 0;
+
+  if (s == 32767UL)
+    return 0;
+  if (s != 32767UL)
+    return 0;
+  if (s < 32767UL)
+    return 0;
+  if (s <= 32767UL)
+    return 0;
+  if (s > 32767UL)
+    return 0;
+  if (s >= 32767UL)
+    return 0;
+
+  if (32767UL == s)
+    return 0;
+  if (32767UL != s)
+    return 0;
+  if (32767UL < s)
+    return 0;
+  if (32767UL <= s)
+    return 0;
+  if (32767UL > s)
+    return 0;
+  if (32767UL >= s)
+    return 0;
+
+  // FIXME: assumes two's complement
+  if (s == -32768L)
+    return 0;
+  if (s != -32768L)
+    return 0;
+  if (s < -32768L)
+    return 0;
+  if (s <= -32768L)
+    return 0;
+  if (s > -32768L)
+    return 0;
+  if (s >= -32768L)
+    return 0;
+
+  if (-32768L == s)
+    return 0;
+  if (-32768L != s)
+    return 0;
+  if (-32768L < s)
+    return 0;
+  if (-32768L <= s)
+    return 0;
+  if (-32768L > s)
+    return 0;
+  if (-32768L >= s)
+    return 0;
+#endif
+
+  if (s == 0)
+    return 0;
+  if (s != 0)
+    return 0;
+  if (s < 0)
+    return 0;
+  if (s <= 0)
+    return 0;
+  if (s > 0)
+    return 0;
+  if (s >= 0)
+    return 0;
+
+  if (0 == s)
+    return 0;
+  if (0 != s)
+    return 0;
+  if (0 < s)
+    return 0;
+  if (0 <= s)
+    return 0;
+  if (0 > s)
+    return 0;
+  if (0 >= s)
+    return 0;
+
+  // However the comparison with 0U would warn
+
+  unsigned short us = value();
+
+#ifdef TEST
+  if (us == 65535)
+      return 0;
+  if (us != 65535)
+      return 0;
+  if (us < 65535)
+      return 0;
+  if (us <= 65535) // expected-warning {{comparison 'unsigned short' <= 65535 is always true}}
+      return 0;
+  if (us > 65535) // expected-warning {{comparison 'unsigned short' > 65535 is always false}}
+      return 0;
+  if (us >= 65535)
+      return 0;
+
+  if (65535 == us)
+      return 0;
+  if (65535 != us)
+      return 0;
+  if (65535 < us) // expected-warning {{comparison 65535 < 'unsigned short' is always false}}
+      return 0;
+  if (65535 <= us)
+      return 0;
+  if (65535 > us)
+      return 0;
+  if (65535 >= us) // expected-warning {{comparison 65535 >= 'unsigned short' is always true}}
+      return 0;
+
+  if (us == 65535UL)
+      return 0;
+  if (us != 65535UL)
+      return 0;
+  if (us < 65535UL)
+      return 0;
+  if (us <= 65535UL) // expected-warning {{comparison 'unsigned short' <= 65535 is always true}}
+      return 0;
+  if (us > 65535UL) // expected-warning {{comparison 'unsigned short' > 65535 is always false}}
+      return 0;
+  if (us >= 65535UL)
+      return 0;
+
+  if (65535UL == us)
+      return 0;
+  if (65535UL != us)
+      return 0;
+  if (65535UL < us) // expected-warning {{comparison 65535 < 'unsigned short' is always false}}
+      return 0;
+  if (65535UL <= us)
+      return 0;
+  if (65535UL > us)
+      return 0;
+  if (65535UL >= us) // expected-warning {{comparison 65535 >= 'unsigned short' is always true}}
+      return 0;
+#else
+  // expected-no-diagnostics
+  if (us == 65535)
+      return 0;
+  if (us != 65535)
+      return 0;
+  if (us < 65535)
+      return 0;
+  if (us <= 65535)
+      return 0;
+  if (us > 65535)
+      return 0;
+  if (us >= 65535)
+      return 0;
+
+  if (65535 == us)
+      return 0;
+  if (65535 != us)
+      return 0;
+  if (65535 < us)
+      return 0;
+  if (65535 <= us)
+      return 0;
+  if (65535 > us)
+      return 0;
+  if (65535 >= us)
+      return 0;
+
+  if (us == 65535UL)
+      return 0;
+  if (us != 65535UL)
+      return 0;
+  if (us < 65535UL)
+      return 0;
+  if (us <= 65535UL)
+      return 0;
+  if (us > 65535UL)
+      return 0;
+  if (us >= 65535UL)
+      return 0;
+
+  if (65535UL == us)
+      return 0;
+  if (65535UL != us)
+      return 0;
+  if (65535UL < us)
+      return 0;
+  if (65535UL <= us)
+      return 0;
+  if (65535UL > us)
+      return 0;
+  if (65535UL >= us)
+      return 0;
+#endif
+
+  if (us == 32767)
+    return 0;
+  if (us != 32767)
+    return 0;
+  if (us < 32767)
+    return 0;
+  if (us <= 32767)
+    return 0;
+  if (us > 32767)
+    return 0;
+  if (us >= 32767)
+    return 0;
+
+  if (32767 == us)
+    return 0;
+  if (32767 != us)
+    return 0;
+  if (32767 < us)
+    return 0;
+  if (32767 <= us)
+    return 0;
+  if (32767 > us)
+    return 0;
+  if (32767 >= us)
+    return 0;
+
+  if (us == 32767UL)
+    return 0;
+  if (us != 32767UL)
+    return 0;
+  if (us < 32767UL)
+    return 0;
+  if (us <= 32767UL)
+    return 0;
+  if (us > 32767UL)
+    return 0;
+  if (us >= 32767UL)
+    return 0;
+
+  if (32767UL == us)
+    return 0;
+  if (32767UL != us)
+    return 0;
+  if (32767UL < us)
+    return 0;
+  if (32767UL <= us)
+    return 0;
+  if (32767UL > us)
+    return 0;
+  if (32767UL >= us)
+    return 0;
+
+#if __SIZEOF_INT128__
+  __int128 i128;
+  if (i128 == -1) // used to crash
+      return 0;
+#endif
+
+
+  enum E {
+  yes,
+  no,
+  maybe
+  };
+  enum E e;
+
+  if (e == yes)
+      return 0;
+  if (e != yes)
+      return 0;
+  if (e < yes)
+      return 0;
+  if (e <= yes)
+      return 0;
+  if (e > yes)
+      return 0;
+  if (e >= yes)
+      return 0;
+
+  if (yes == e)
+      return 0;
+  if (yes != e)
+      return 0;
+  if (yes < e)
+      return 0;
+  if (yes <= e)
+      return 0;
+  if (yes > e)
+      return 0;
+  if (yes >= e)
+      return 0;
+
+  if (e == maybe)
+      return 0;
+  if (e != maybe)
+      return 0;
+  if (e < maybe)
+      return 0;
+  if (e <= maybe)
+      return 0;
+  if (e > maybe)
+      return 0;
+  if (e >= maybe)
+      return 0;
+
+  if (maybe == e)
+      return 0;
+  if (maybe != e)
+      return 0;
+  if (maybe < e)
+      return 0;
+  if (maybe <= e)
+      return 0;
+  if (maybe > e)
+      return 0;
+  if (maybe >= e)
+      return 0;
+
+  return 1;
+}