[NFC] [scudo] syntax-check DCHECK arguments if DCHECK is off

[fmayer]

Summary

This is a widespread technique, used in at least:

• ABSL: https://github.com/abseil/abseil-cpp/blob/master/absl/log/internal/check_op.h#L52
• Chromium: https://source.chromium.org/chromium/chromium/src/+/main:base/check.h;l=185?q=DCHECK%20f:base&ss=chromium
• Android: https://cs.android.com/android/platform/superproject/+/master:system/libbase/include/android-base/logging.h;drc=bda7f0a0cc945c860713a1dc497919f17fad1651;l=321

[Chia-hungDuan]

compiler-rt/lib/scudo/standalone/internal_defs.h

139

Will it be better to have parenthesis? like (A) == (B)

[fmayer]

update

[vitalybuka]

isn't this to suppress unused warnings?

then we will miss stuff like:
auto t = long_calculation();
DHCECK(t, expected);

[fmayer]

In D141713#4052899, @vitalybuka wrote:

isn't this to suppress unused warnings?

then we will miss stuff like:
auto t = long_calculation();
DHCECK(t, expected);

Not sure what exactly you mean, but yes, in that particular case the unused warning shouldn't fire anymore.

[vitalybuka]

In D141713#4053009, @fmayer wrote:

In D141713#4052899, @vitalybuka wrote:

isn't this to suppress unused warnings?

then we will miss stuff like:
auto t = long_calculation();
DHCECK(t, expected);

Not sure what exactly you mean, but yes, in that particular case the unused warning shouldn't fire anymore.

CONS: seeing "unused warning" there is not a bug, but useful features.
PROS: complication of expression in release build to get error early is useful too.

so rather LGTM

compiler-rt/lib/scudo/standalone/internal_defs.h

 #define DCHECK_NE(A, B) CHECK_NE(A, B)
 #define DCHECK_LT(A, B) CHECK_LT(A, B)
 #define DCHECK_LE(A, B) CHECK_LE(A, B)
 #define DCHECK_GT(A, B) CHECK_GT(A, B)
 #define DCHECK_GE(A, B) CHECK_GE(A, B)
 #else
 #define DCHECK(A)                                                              \
   do {                                                                         \
-  } while (false)
+  } while (false && A)
 #define DCHECK_EQ(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A == B)
 #define DCHECK_NE(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A != B)
 #define DCHECK_LT(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A < B)
 #define DCHECK_LE(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A <= B)
 #define DCHECK_GT(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A > B)
 #define DCHECK_GE(A, B)                                                        \
   do {                                                                         \
-  } while (false)
+  } while (false && A >= B)
 #endif
 
 // The superfluous die() call effectively makes this macro NORETURN.
 #define UNREACHABLE(Msg)                                                       \
   do {                                                                         \
     CHECK(0 && Msg);                                                           \
     die();                                                                     \
   } while (0)
 
 } // namespace scudo
 
 #endif // SCUDO_INTERNAL_DEFS_H_