[LibFuzzer] Tweak `MutationDispatcher::Mutate_CopyPart` mutation.
It doesn't make sense to non-deterministically choose between
`CopyPart(..)` and `InsertPart(..)` when it is known that
`InsertPart(..)` will fail.
This upstream's a change from JFS solver's fork of LibFuzzer.
Differential Revision: https://reviews.llvm.org/D45693
llvm-svn: 330687
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
index e0e4578..865e598 100644
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
@@ -339,7 +339,9 @@
size_t MutationDispatcher::Mutate_CopyPart(uint8_t *Data, size_t Size,
size_t MaxSize) {
if (Size > MaxSize || Size == 0) return 0;
- if (Rand.RandBool())
+ // If Size == MaxSize, `InsertPartOf(...)` will
+ // fail so there's no point using it in this case.
+ if (Size == MaxSize || Rand.RandBool())
return CopyPartOf(Data, Size, Data, Size);
else
return InsertPartOf(Data, Size, Data, Size, MaxSize);