[windows] Don't inline fieldFromInstruction on Windows

Summary:
The VS compiler (on Windows) has a bug which results in fieldFromInstruction being optimized out in some circumstances. This only happens in *release no debug info* builds that have assertions *turned off* - in all other situations the function is not inlined, so the functionality is correct. All of the bots have assertions turned on, so this path is not regularly tested. The workaround is to not inline the function on Windows - if the bug is fixed in a later release of the VS compiler, the noinline specification can be removed.

The test that consistently reproduces this is Lanai v11.txt test.

Reviewers: asmith, labath, zturner

Subscribers: dblaikie, stella.stamenova, aprantl, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D49753

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337942 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/utils/TableGen/FixedLenDecoderEmitter.cpp b/utils/TableGen/FixedLenDecoderEmitter.cpp
index 9628c47ac074fd8a8beea43147da8cb0e93a001b..76ba1c001092a7bc9e5233c3ea36f18041ffa2a0 100644 (file)
--- a/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -2063,10 +2063,16 @@ static bool populateInstruction(CodeGenTarget &Target,
 
 // emitFieldFromInstruction - Emit the templated helper function
 // fieldFromInstruction().
+// On Windows we make sure that this function is not inlined when
+// using the VS compiler. It has a bug which causes the function
+// to be optimized out in some circustances. See llvm.org/pr38292
 static void emitFieldFromInstruction(formatted_raw_ostream &OS) {
   OS << "// Helper function for extracting fields from encoded instructions.\n"
      << "template<typename InsnType>\n"
-   << "static InsnType fieldFromInstruction(InsnType insn, unsigned startBit,\n"
+     << "#if defined(_MSC_VER) && !defined(__clang__)\n"
+     << "__declspec(noinline)\n"
+     << "#endif\n"
+     << "static InsnType fieldFromInstruction(InsnType insn, unsigned startBit,\n"
      << "                                     unsigned numBits) {\n"
      << "    assert(startBit + numBits <= (sizeof(InsnType)*8) &&\n"
      << "           \"Instruction field out of bounds!\");\n"