UseListOrder: Visit global values

When predicting use-list order, we visit functions in reverse order
followed by `GlobalValue`s and write out use-lists at the first
opportunity.  In the reader, this will translate to *after* the last use
has been added.

For this to work, we actually need to descend into `GlobalValue`s.
Added a targeted test in `use-list-order.ll` and `RUN` lines to the
newly passing tests in `test/Bitcode`.

There are two remaining failures in `test/Bitcode`:

  - blockaddress.ll: I haven't thought through how to model the way
    block addresses change the order of use-lists (or how to work around
    it).

  - metadata-2.ll: There's an old-style `@llvm.used` global array here
    that I suspect the .ll parser isn't upgrading properly.  When it
    round-trips through bitcode, the .bc reader *does* upgrade it, so
    the extra variable (`i8* null`) has an extra use, and the shuffle
    vector doesn't match.

    I think the fix is to upgrade old-style global arrays (or reject
    them?) in the .ll parser.

This is part of PR5680.

llvm-svn: 214321

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
index c05d6ae0d21..fa1c8b3c57d 100644
--- a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -211,9 +211,9 @@ static void predictValueUseListOrder(const Value *V, const Function *F,
 
   // Recursive descent into constants.
   if (const Constant *C = dyn_cast<Constant>(V))
-    if (C->getNumOperands() && !isa<GlobalValue>(C))
+    if (C->getNumOperands()) // Visit GlobalValues.
       for (const Value *Op : C->operands())
-        if (isa<Constant>(Op) && !isa<GlobalValue>(Op))
+        if (isa<Constant>(Op)) // Visit GlobalValues.
           predictValueUseListOrder(Op, F, OM, Stack);
 }
 
@@ -241,8 +241,7 @@ static UseListOrderStack predictUseListOrder(const Module *M) {
     for (const BasicBlock &BB : F)
       for (const Instruction &I : BB)
         for (const Value *Op : I.operands())
-          if ((isa<Constant>(*Op) && !isa<GlobalValue>(*Op)) ||
-              isa<InlineAsm>(*Op))
+          if (isa<Constant>(*Op) || isa<InlineAsm>(*Op)) // Visit GlobalValues.
             predictValueUseListOrder(Op, &F, OM, Stack);
     for (const BasicBlock &BB : F)
       for (const Instruction &I : BB)