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Diffstat (limited to 'llvm/docs/LangRef.rst')
| -rw-r--r-- | llvm/docs/LangRef.rst | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index b953dbd0f17..e0610974f30 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -3245,6 +3245,17 @@ match what was already there. However, a store *to* an undefined location could clobber arbitrary memory, therefore, it has undefined behavior. +**MemorySanitizer**, a detector of uses of uninitialized memory, +defines a branch with condition that depends on an undef value (or +certain other values, like e.g. a result of a load from heap-allocated +memory that has never been stored to) to have an externally visible +side effect. For this reason functions with *sanitize_memory* +attribute are not allowed to produce such branches "out of thin +air". More strictly, an optimization that inserts a conditional branch +is only valid if in all executions where the branch condition has at +least one undefined bit, the same branch condition is evaluated in the +input IR as well. + .. _poisonvalues: Poison Values |
