Add a comment which explains why the assert fired and how to fix it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166467 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/VMCore/TargetTransformInfo.cpp b/lib/VMCore/TargetTransformInfo.cpp
index 3af0222a211a280738928c2b3cf23a0d1fafb4f1..219d24c1f567648f2535f517661f2b003f76bd6c 100644 (file)
--- a/lib/VMCore/TargetTransformInfo.cpp
+++ b/lib/VMCore/TargetTransformInfo.cpp
@@ -17,6 +17,10 @@ using namespace llvm;
 /// @note This has to exist, because this is a pass, but it should never be
 /// used.
 TargetTransformInfo::TargetTransformInfo() : ImmutablePass(ID) {
+  /// You are seeing this error because your pass required the TTI
+  /// using a call to "getAnalysis<TargetTransformInfo>()", and you did
+  /// not initialize a machine target which can provide the TTI.
+  /// You should use "getAnalysisIfAvailable<TargetTransformInfo>()" instead.
   report_fatal_error("Bad TargetTransformInfo ctor used.  "
                      "Tool did not specify a TargetTransformInfo to use?");
 }