Add a comment about why ScalarEvolution doesn't recognize non-loop PHIs
even when they're obvious.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75632 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 0152a9f..457466f 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2402,6 +2402,10 @@
return SymbolicName;
}
+ // It's tempting to recognize PHIs with a unique incoming value, however
+ // this leads passes like indvars to break LCSSA form. Fortunately, such
+ // PHIs are rare, as instcombine zaps them.
+
// If it's not a loop phi, we can't handle it yet.
return getUnknown(PN);
}