[ThinLTO] Fix assertions on lazy-loading of Metadata TBAA attachments

Summary:
The issue happens with:

 %0 = ....., !tbaa !0
 %1 = ....., !tbaa !1

With !0 that references !1.

In this case when loading !0 we generates a temporary for the
operand !1. We now flush it immediately and trigger the load of
!1 before moving on. If we don't we get the temporary when
attaching to %1. This is usually not an issue except that we
eagerly try to update TBAA MDNodes, which is obviously not possible
if we only have a temporary.

Differential Revision: https://reviews.llvm.org/D28423

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291362 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/MetadataLoader.cpp

@@ -1562,8 +1562,6 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadataAttachment(
 
   SmallVector<uint64_t, 64> Record;
 
-  PlaceholderQueue Placeholders;
-
   while (true) {
     BitstreamEntry Entry = Stream.advanceSkippingSubblocks();
 
@@ -1572,7 +1570,6 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadataAttachment(
     case BitstreamEntry::Error:
       return error("Malformed block");
     case BitstreamEntry::EndBlock:
-      resolveForwardRefsAndPlaceholders(Placeholders);
       return Error::success();
     case BitstreamEntry::Record:
       // The interesting case.
@@ -1608,10 +1605,13 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadataAttachment(
 
         auto Idx = Record[i + 1];
         if (Idx < (MDStringRef.size() + GlobalMetadataBitPosIndex.size()) &&
-            !MetadataList.lookup(Idx))
+            !MetadataList.lookup(Idx)) {
           // Load the attachment if it is in the lazy-loadable range and hasn't
           // been loaded yet.
+          PlaceholderQueue Placeholders;
           lazyLoadOneMetadata(Idx, Placeholders);
+          resolveForwardRefsAndPlaceholders(Placeholders);
+        }
 
         Metadata *Node = MetadataList.getMetadataFwdRef(Idx);
         if (isa<LocalAsMetadata>(Node))

test/ThinLTO/X86/Inputs/funcimport-tbaa.ll

@@ -0,0 +1,11 @@
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+
+define i32 @main() {
+entry:
+  %unused = call float @globalfunc1(i32* null, float*null)
+  ret i32 0
+}
+
+declare float @globalfunc1(i32*, float*)

test/ThinLTO/X86/funcimport-tbaa.ll

@@ -0,0 +1,38 @@
+; We generate invalid TBAA, hence -disable-verify, but this is a convenient way
+; to trigger a metadata lazyloading crash
+
+; RUN: opt -module-summary %s -o %t.bc -bitcode-mdindex-threshold=0 -disable-verify
+; RUN: opt -module-summary %p/Inputs/funcimport-tbaa.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t3.bc %t.bc %t2.bc
+
+
+; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t3.bc -o - \
+; RUN:  | llvm-dis -o - | FileCheck %s --check-prefix=IMPORTGLOB1
+; IMPORTGLOB1: define available_externally float @globalfunc1
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define float @globalfunc1(i32*, float*) {
+  %3 = load i32, i32* %0, align 4, !tbaa !0
+  %4 = sitofp i32 %3 to float
+  %5 = load float, float* %1, align 4, !tbaa !4
+  %6 = fadd float %4, %5
+  ret float %6
+}
+
+; We need a second function for force the metadata to be emitted in the global block
+define float @globalfunc2(i32*, float*) {
+  %3 = load i32, i32* %0, align 4, !tbaa !0
+  %4 = sitofp i32 %3 to float
+  %5 = load float, float* %1, align 4, !tbaa !4
+  %6 = fadd float %4, %5
+  ret float %6
+}
+
+!0 = !{!1, !4, i64 0}
+!1 = !{!"int", !2, i64 0}
+!2 = !{!"omnipotent char", !3, i64 0}
+!3 = !{!"Simple C/C++ TBAA"}
+!4 = !{!5, !5, i64 0}
+!5 = !{!"float", !2, i64 0}