Make the unreachable probability much much heavier. The previous

probability wouldn't be considered "hot" in some weird loop structures
or other compounding probability patterns. This makes it much harder to
confuse, but isn't really a principled fix. I'd actually like it if we
could model a zero probability, as it would make this much easier to
reason about. Suggestions for how to do this better are welcome.

llvm-svn: 147142

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index f9461c0b853..2730ce6c63b 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -65,8 +65,9 @@ static const uint32_t UR_TAKEN_WEIGHT = 1;
 ///
 /// This is the weight for a branch not being taken toward a block that
 /// terminates (eventually) in unreachable. Such a branch is essentially never
-/// taken.
-static const uint32_t UR_NONTAKEN_WEIGHT = 1023;
+/// taken. Set the weight to an absurdly high value so that nested loops don't
+/// easily subsume it.
+static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
 
 static const uint32_t PH_TAKEN_WEIGHT = 20;
 static const uint32_t PH_NONTAKEN_WEIGHT = 12;