=?utf-8?q?Félix?= Cloutier <[email protected]>,
=?utf-8?q?Félix?= Cloutier <[email protected]>,
=?utf-8?q?Félix?= Cloutier <[email protected]>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/[email protected]>
================
@@ -2312,6 +2312,30 @@ are listed below.
additional function arity information (for supported targets). See
:doc:`ControlFlowIntegrity` for more details.
+.. option:: -fstrict-bool
+
+ ``bool`` values are stored to memory as 8-bit values on most targets. C and
+ C++ specify that it is undefined behavior to put a value other than 0 or 1
+ in the storage of a ``bool`` value, and with ``-fstrict-bool``, Clang
+ leverages this knowledge for optimization opportunities. When this
+ assumption is violated, for instance if invalid data is ``memcpy``ed over a
+ ``bool``, the optimized code can lead to memory corruption.
+ ``-fstrict-bool`` is enabled by default.
+
+.. option:: -fno-strict-bool[={truncate|nonzero}]
+
+ Disable optimizations based on the assumption that all ``bool`` values,
+ which are typically represented as 8-bit integers in memory, only ever
+ contain bit patterns 0 or 1. When ``=truncate`` is specified, a ``bool`` is
+ true if its least significant bit is set, and false otherwise. When
+ ``=nonzero`` is specified, a ``bool`` is true when any bit is set, and
+ false otherwise. The default is ``=truncate``, but this could change in
+ future releases.
+
+ ``-fno-strict-bool`` does not permit Clang to store a value other than 0 or
----------------
AaronBallman wrote:
It would be nice to mention whether UBSan will still catch violations even if
`-fno-strict-bool` is passed.
https://github.com/llvm/llvm-project/pull/160790
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