From 76e007e7e388ba700b3adc1551d88f1ba442a30f Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Tue, 11 Oct 2016 18:17:26 +0000 Subject: [PATCH] [Support] Fix undefined behavior in RandomNumberGenerator. This has existed pretty much forever AFAICT, but the code was never being exercised because nobody was using the class. A user of this class surfaced, and now we're breaking with UB. The code was obviously wrong, so it's fixed here. llvm-svn: 283912 --- llvm/lib/Support/RandomNumberGenerator.cpp | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Support/RandomNumberGenerator.cpp b/llvm/lib/Support/RandomNumberGenerator.cpp index d340764..8ea02d7 100644 --- a/llvm/lib/Support/RandomNumberGenerator.cpp +++ b/llvm/lib/Support/RandomNumberGenerator.cpp @@ -47,11 +47,11 @@ RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) { // are using a 64-bit RNG. This isn't a problem since the Mersenne // twister constructor copies these correctly into its initial state. std::vector Data; - Data.reserve(2 + Salt.size()); - Data.push_back(Seed); - Data.push_back(Seed >> 32); + Data.resize(2 + Salt.size()); + Data[0] = Seed; + Data[1] = Seed >> 32; - std::copy(Salt.begin(), Salt.end(), Data.end()); + std::copy(Salt.begin(), Salt.end(), Data.begin() + 2); std::seed_seq SeedSeq(Data.begin(), Data.end()); Generator.seed(SeedSeq); -- 2.7.4