[msan] A comment on ICmp handling logic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173453 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 64882c284b3ee0e1ddda690db54d610874bd1f7a..a329dcc6bee2a241a0777a79c3685b8e4614be0c 100644 (file)
--- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -1211,6 +1211,9 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     A = IRB.CreatePointerCast(A, Sa->getType());
     B = IRB.CreatePointerCast(B, Sb->getType());
 
+    // Let [a0, a1] be the interval of possible values of A, taking into account
+    // its undefined bits. Let [b0, b1] be the interval of possible values of B.
+    // Then (A cmp B) is defined iff (a0 cmp b1) == (a1 cmp b0).
     bool IsSigned = I.isSigned();
     Value *S1 = IRB.CreateICmp(I.getPredicate(),
                                getLowestPossibleValue(IRB, A, Sa, IsSigned),