Handle value uses wrapped in metadata for the use-list order

When generating the use-list order, also consider value uses that are
operands which are wrapped in metadata; e.g. llvm.dbg.value operands.

This fixes PR36778. The test case is based on the reproducer from that
report.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D53758

lib/Bitcode/Writer/ValueEnumerator.cpp

@@ -78,6 +78,16 @@ struct OrderMap {
 
 } // end anonymous namespace
 
+/// Look for a value that might be wrapped as metadata, e.g. a value in a
+/// metadata operand. Returns nullptr for a non-wrapped input value if
+/// OnlyWrapped is true, or it returns the input value as-is if false.
+static const Value *skipMetadataWrapper(const Value *V, bool OnlyWrapped) {
+  if (const auto *MAV = dyn_cast<MetadataAsValue>(V))
+    if (const auto *VAM = dyn_cast<ValueAsMetadata>(MAV->getMetadata()))
+      return VAM->getValue();
+  return OnlyWrapped ? nullptr : V;
+}
+
 static void orderValue(const Value *V, OrderMap &OM) {
   if (OM.lookup(V).first)
     return;
@@ -123,6 +133,25 @@ static OrderMap orderModule(const Module &M) {
       if (!isa<GlobalValue>(U.get()))
         orderValue(U.get(), OM);
   }
+
+  // As constants used in metadata operands are emitted as module-level
+  // constants, we must order them before other operands. Also, we must order
+  // these before global values, as these will be read before setting the
+  // global values' initializers. The latter matters for constants which have
+  // uses towards other constants that are used as initializers.
+  for (const Function &F : M) {
+    if (F.isDeclaration())
+      continue;
+    for (const BasicBlock &BB : F)
+      for (const Instruction &I : BB)
+        for (const Value *V : I.operands()) {
+          if (const Value *Op = skipMetadataWrapper(V, true)) {
+            if ((isa<Constant>(*Op) && !isa<GlobalValue>(*Op)) ||
+                isa<InlineAsm>(*Op))
+              orderValue(Op, OM);
+          }
+        }
+  }
   OM.LastGlobalConstantID = OM.size();
 
   // Initializers of GlobalValues are processed in

lib/IR/AsmWriter.cpp

@@ -116,6 +116,15 @@ struct OrderMap {
 
 } // end anonymous namespace
 
+/// Look for a value that might be wrapped as metadata, e.g. a value in a
+/// metadata operand. Returns the input value as-is if it is not wrapped.
+static const Value *skipMetadataWrapper(const Value *V) {
+  if (const auto *MAV = dyn_cast<MetadataAsValue>(V))
+    if (const auto *VAM = dyn_cast<ValueAsMetadata>(MAV->getMetadata()))
+      return VAM->getValue();
+  return V;
+}
+
 static void orderValue(const Value *V, OrderMap &OM) {
   if (OM.lookup(V).first)
     return;
@@ -132,8 +141,6 @@ static void orderValue(const Value *V, OrderMap &OM) {
 }
 
 static OrderMap orderModule(const Module *M) {
-  // This needs to match the order used by ValueEnumerator::ValueEnumerator()
-  // and ValueEnumerator::incorporateFunction().
   OrderMap OM;
 
   for (const GlobalVariable &G : M->globals()) {
@@ -167,10 +174,12 @@ static OrderMap orderModule(const Module *M) {
     for (const BasicBlock &BB : F) {
       orderValue(&BB, OM);
       for (const Instruction &I : BB) {
-        for (const Value *Op : I.operands())
+        for (const Value *Op : I.operands()) {
+          Op = skipMetadataWrapper(Op);
           if ((isa<Constant>(*Op) && !isa<GlobalValue>(*Op)) ||
               isa<InlineAsm>(*Op))
             orderValue(Op, OM);
+        }
         orderValue(&I, OM);
       }
     }
@@ -284,9 +293,11 @@ static UseListOrderStack predictUseListOrder(const Module *M) {
       predictValueUseListOrder(&A, &F, OM, Stack);
     for (const BasicBlock &BB : F)
       for (const Instruction &I : BB)
-        for (const Value *Op : I.operands())
+        for (const Value *Op : I.operands()) {
+          Op = skipMetadataWrapper(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)
         predictValueUseListOrder(&I, &F, OM, Stack);

test/Assembler/metadata-use-uselistorder.ll

@@ -0,0 +1,58 @@
+; RUN: verify-uselistorder %s
+
+; Reproducer for PR36778.
+
+; Verify that uses in metadata operands are considered when generating the
+; use-list order. In this case the use-list order for @global_arr was not
+; correctly preserved due to the uses in the dbg.value contant expressions not
+; being considered, since they are wrapped in metadata.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@global = local_unnamed_addr global i64 0, align 8
+@global_arr = common local_unnamed_addr global [10 x i64] zeroinitializer, align 16
+
+define void @foo() local_unnamed_addr !dbg !6 {
+entry:
+  %0 = load i64, i64* getelementptr inbounds ([10 x i64], [10 x i64]* @global_arr, i64 0, i64 4), align 16
+  call void @llvm.dbg.value(metadata i64* getelementptr inbounds ([10 x i64], [10 x i64]* @global_arr, i64 0, i64 5), metadata !10, metadata !DIExpression()), !dbg !13
+  %1 = load i64, i64* getelementptr inbounds ([10 x i64], [10 x i64]* @global_arr, i64 0, i64 6), align 16
+  call void @llvm.dbg.value(metadata i64* getelementptr inbounds ([10 x i64], [10 x i64]* @global_arr, i64 0, i64 6), metadata !10, metadata !DIExpression()), !dbg !14
+  ret void
+}
+
+define void @bar() local_unnamed_addr !dbg !15 {
+entry:
+  call void @llvm.dbg.value(metadata i64* getelementptr inbounds ([10 x i64], [10 x i64]* @global_arr, i64 0, i64 7), metadata !17, metadata !DIExpression()), !dbg !18
+  ret void
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+
+attributes #0 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !2, nameTableKind: None)
+!1 = !DIFile(filename: "uses.c", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 8.0.0"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 6, type: !7, isLocal: false, isDefinition: true, scopeLine: 6, isOptimized: true, unit: !0, retainedNodes: !9)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null}
+!9 = !{!10}
+!10 = !DILocalVariable(name: "local1", scope: !6, file: !1, line: 7, type: !11)
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!13 = !DILocation(line: 8, column: 8, scope: !6)
+!14 = !DILocation(line: 7, column: 9, scope: !6)
+!15 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 12, type: !7, isLocal: false, isDefinition: true, scopeLine: 12, isOptimized: true, unit: !0, retainedNodes: !16)
+!16 = !{!17}
+!17 = !DILocalVariable(name: "local2", scope: !15, file: !1, line: 13, type: !11)
+!18 = !DILocation(line: 14, column: 1, scope: !15)

tools/verify-uselistorder/verify-uselistorder.cpp

@@ -224,12 +224,18 @@ ValueMapping::ValueMapping(const Module &M) {
     // Constants used by instructions.
     for (const BasicBlock &BB : F)
       for (const Instruction &I : BB)
-        for (const Value *Op : I.operands())
+        for (const Value *Op : I.operands()) {
+          // Look through a metadata wrapper.
+          if (const auto *MAV = dyn_cast<MetadataAsValue>(Op))
+            if (const auto *VAM = dyn_cast<ValueAsMetadata>(MAV->getMetadata()))
+              Op = VAM->getValue();
+
           if ((isa<Constant>(Op) && !isa<GlobalValue>(*Op)) ||
               isa<InlineAsm>(Op))
             map(Op);
         }
   }
+}
 
 void ValueMapping::map(const Value *V) {
   if (IDs.lookup(V))
@@ -500,11 +506,16 @@ static void changeUseLists(Module &M, Changer changeValueUseList) {
     // Constants used by instructions.
     for (BasicBlock &BB : F)
       for (Instruction &I : BB)
-        for (Value *Op : I.operands())
+        for (Value *Op : I.operands()) {
+          // Look through a metadata wrapper.
+          if (auto *MAV = dyn_cast<MetadataAsValue>(Op))
+            if (auto *VAM = dyn_cast<ValueAsMetadata>(MAV->getMetadata()))
+              Op = VAM->getValue();
           if ((isa<Constant>(Op) && !isa<GlobalValue>(*Op)) ||
               isa<InlineAsm>(Op))
             changeValueUseList(Op);
         }
+  }
 
   if (verifyModule(M, &errs()))
     report_fatal_error("verification failed");