Recommit "[BitcodeReader] Validate OpNum, before accessing Record array."

This recommits r365750 (git commit 8b222ecf27)

Original message:

   Currently invalid bitcode files can cause a crash, when OpNum exceeds
   the number of elements in Record, like in the attached bitcode file.

   The test case was generated by clusterfuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=15698

   Reviewers: t.p.northover, thegameg, jfb

   Reviewed By: jfb

   Differential Revision: https://reviews.llvm.org/D64507

   llvm-svn: 365750jkkkk

llvm-svn: 366018

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -4171,6 +4171,10 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo, LHS->getType(), RHS))
         return error("Invalid record");
 
+      if (OpNum >= Record.size())
+        return error(
+            "Invalid record: operand number exceeded available operands");
+
       unsigned PredVal = Record[OpNum];
       bool IsFP = LHS->getType()->isFPOrFPVectorTy();
       FastMathFlags FMF;

llvm/test/Bitcode/invalid.test

@@ -235,3 +235,8 @@ RUN: not llvm-dis -disable-output %p/Inputs/invalid-nonpointer-atomicrmw.bc 2>&1
 RUN:   FileCheck --check-prefix=NONPOINTER-ATOMICRMW %s
 
 NONPOINTER-ATOMICRMW: Invalid record
+
+RUN: not llvm-dis -disable-output %p/Inputs/invalid-fcmp-opnum.bc 2>&1 | \
+RUN:   FileCheck --check-prefix=INVALID-FCMP-OPNUM %s
+
+INVALID-FCMP-OPNUM: Invalid record: operand number exceeded available operands