[BlockExtractor] Avoid assert with wrong line format

[jsji]

Summary

When the line format is wrong, we may end up accessing out of bound
memory. eg: the test with invalide line will cause assert.
Assertion `idx < size()' failed

The fix is to report fatal when we found mismatched line format.

llvm/trunk/lib/Transforms/IPO/BlockExtractor.cpp

void BlockExtractor::loadFile() {
   Buf->getBuffer().split(Lines, '\n', /*MaxSplit=*/-1,
                          /*KeepEmpty=*/false);
   for (const auto &Line : Lines) {
     SmallVector<StringRef, 4> LineSplit;
     Line.split(LineSplit, ' ', /*MaxSplit=*/-1,
                /*KeepEmpty=*/false);
     if (LineSplit.empty())
       continue;
+    if (LineSplit.size()!=2)
+      report_fatal_error("Invalid line format, expecting lines like: 'funcname bb1[;bb2..]'");
     SmallVector<StringRef, 4> BBNames;
     LineSplit[1].split(BBNames, ';', /*MaxSplit=*/-1,
                        /*KeepEmpty=*/false);
     if (BBNames.empty())
       report_fatal_error("Missing bbs name");
     BlocksByName.push_back({LineSplit[0], {BBNames.begin(), BBNames.end()}});
   }
 }

llvm/trunk/test/Transforms/BlockExtractor/invalid-line.ll

+; RUN: echo 'foo' > %t
+; RUN: not opt -S -extract-blocks -extract-blocks-file=%t %s 2>&1 | FileCheck %s
+
+; CHECK: Invalid line
+define void @bar() {
+bb:
+  ret void
+}
+