ValueMapper: Disallow metadata mapping recursion through mapValue

This adds an assertion to maintain the property from r265273.  When
Mapper::mapSimpleMetadata calls Mapper::mapValue, it should not find its
way back to mapMetadataImpl.  This guarantees that mapSimpleMetadata is
not involved in any recursion.

Since Mapper::mapValue calls out to arbitrary materializers, we need to
save a bit on the ValueMap to make this assertion effective.

There should be no functionality change here.  This co-recursion should
already have been impossible.

llvm-svn: 265276

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 64ba98e55c9..78f4618aef9 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -379,7 +379,11 @@ Optional<Metadata *> Mapper::mapSimpleMetadata(const Metadata *MD) {
       return mapToSelf(MD);
 
   if (const auto *VMD = dyn_cast<ValueAsMetadata>(MD)) {
+    // Disallow recursion into metadata mapping through mapValue.
+    VM.disableMapMetadata();
     Value *MappedV = mapValue(VMD->getValue());
+    VM.enableMapMetadata();
+
     if (VMD->getValue() == MappedV ||
         (!MappedV && (Flags & RF_IgnoreMissingEntries)))
       return mapToSelf(MD);
@@ -406,6 +410,7 @@ Optional<Metadata *> Mapper::mapSimpleMetadata(const Metadata *MD) {
 }
 
 Metadata *Mapper::mapMetadataImpl(const Metadata *MD) {
+  assert(VM.mayMapMetadata() && "Unexpected co-recursion through mapValue");
   if (Optional<Metadata *> NewMD = mapSimpleMetadata(MD))
     return *NewMD;