[IR] Add verifier support for llvm.module.flags.

- Also, update the LangRef documentation on module flags to match the
   implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172498 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -2462,14 +2462,16 @@ Each triplet has the following form:
    (or more) metadata with the same ID. The supported behaviors are
    described below.
 -  The second element is a metadata string that is a unique ID for the
-   metadata. How each ID is interpreted is documented below.
+   metadata. Each module may only have one flag entry for each unique ID (not
+   including entries with the **Require** behavior).
 -  The third element is the value of the flag.
 
 When two (or more) modules are merged together, the resulting
-``llvm.module.flags`` metadata is the union of the modules'
-``llvm.module.flags`` metadata. The only exception being a flag with the
-*Override* behavior, which may override another flag's value (see
-below).
+``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
+each unique metadata ID string, there will be exactly one entry in the merged
+modules ``llvm.module.flags`` metadata table, and the value for that entry will
+be determined by the merge behavior flag, as described below. The only exception
+is that entries with the *Require* behavior are always preserved.
 
 The following behaviors are supported:
 
@@ -2482,25 +2484,33 @@ The following behaviors are supported:
 
    * - 1
      - **Error**
-           Emits an error if two values disagree. It is an error to have an
-           ID with both an Error and a Warning behavior.
+           Emits an error if two values disagree, otherwise the resulting value
+           is that of the operands.
 
    * - 2
      - **Warning**
-           Emits a warning if two values disagree.
+           Emits a warning if two values disagree. The result value will be the
+           operand for the flag from the first module being linked.
 
    * - 3
      - **Require**
-           Emits an error when the specified value is not present or doesn't
-           have the specified value. It is an error for two (or more)
-           ``llvm.module.flags`` with the same ID to have the Require behavior
-           but different values. There may be multiple Require flags per ID.
+           Adds a requirement that another module flag be present and have a
+           specified value after linking is performed. The value must be a
+           metadata pair, where the first element of the pair is the ID of the
+           module flag to be restricted, and the second element of the pair is
+           the value the module flag should be restricted to. This behavior can
+           be used to restrict the allowable results (via triggering of an
+           error) of linking IDs with the **Override** behavior.
 
    * - 4
      - **Override**
-           Uses the specified value if the two values disagree. It is an
-           error for two (or more) ``llvm.module.flags`` with the same ID
-           to have the Override behavior but different values.
+           Uses the specified value, regardless of the behavior or value of the
+           other module. If both modules specify **Override**, but the values
+           differ, an error will be emitted.
+
+It is an error for a particular unique flag ID to have multiple behaviors,
+except in the case of **Require** (which adds restrictions on another metadata
+value) or **Override**.
 
 An example of module flags:
 
@@ -2522,7 +2532,7 @@ An example of module flags:
 
 -  Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
    behavior if two or more ``!"bar"`` flags are seen is to use the value
-   '37' if their values are not equal.
+   '37'.
 
 -  Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
    behavior if two or more ``!"qux"`` flags are seen is to emit a
@@ -2534,10 +2544,9 @@ An example of module flags:
 
        metadata !{ metadata !"foo", i32 1 }
 
-   The behavior is to emit an error if the ``llvm.module.flags`` does
-   not contain a flag with the ID ``!"foo"`` that has the value '1'. If
-   two or more ``!"qux"`` flags exist, then they must have the same
-   value or an error will be issued.
+   The behavior is to emit an error if the ``llvm.module.flags`` does not
+   contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
+   performed.
 
 Objective-C Garbage Collection Module Flags Metadata
 ----------------------------------------------------

lib/IR/Verifier.cpp

@@ -200,6 +200,8 @@ namespace {
            E = M.named_metadata_end(); I != E; ++I)
         visitNamedMDNode(*I);
 
+      visitModuleFlags(M);
+
       // If the module is broken, abort at this time.
       return abortIfBroken();
     }
@@ -240,6 +242,8 @@ namespace {
     void visitGlobalAlias(GlobalAlias &GA);
     void visitNamedMDNode(NamedMDNode &NMD);
     void visitMDNode(MDNode &MD, Function *F);
+    void visitModuleFlags(Module &M);
+    void visitModuleFlag(MDNode *Op, SmallSetVector<MDString*, 16> &SeenIDs);
     void visitFunction(Function &F);
     void visitBasicBlock(BasicBlock &BB);
     using InstVisitor<Verifier>::visit;
@@ -521,6 +525,59 @@ void Verifier::visitMDNode(MDNode &MD, Function *F) {
   }
 }
 
+void Verifier::visitModuleFlags(Module &M) {
+  const NamedMDNode *Flags = M.getModuleFlagsMetadata();
+  if (!Flags) return;
+
+  // Scan each flag.
+  SmallSetVector<MDString*, 16> SeenIDs;
+  for (unsigned I = 0, E = Flags->getNumOperands(); I != E; ++I) {
+    visitModuleFlag(Flags->getOperand(I), SeenIDs);
+  }
+}
+
+void Verifier::visitModuleFlag(MDNode *Op, 
+                               SmallSetVector<MDString*, 16> &SeenIDs) {
+  // Each module flag should have three arguments, the merge behavior (a
+  // constant int), the flag ID (an MDString), and the value.
+  Assert1(Op->getNumOperands() == 3,
+          "incorrect number of operands in module flag", Op);
+  ConstantInt *Behavior = dyn_cast<ConstantInt>(Op->getOperand(0));
+  MDString *ID = dyn_cast<MDString>(Op->getOperand(1));
+  Assert1(Behavior,
+          "invalid behavior operand in module flag (expected constant integer)",
+          Op->getOperand(0));
+  unsigned BehaviorValue = Behavior->getZExtValue();
+  Assert1((Module::Error <= BehaviorValue &&
+           BehaviorValue <= Module::Override),
+          "invalid behavior operand in module flag (unexpected constant)",
+          Op->getOperand(0));
+  Assert1(ID,
+          "invalid ID operand in module flag (expected metadata string)",
+          Op->getOperand(1));
+
+  // Unless this is a "requires" flag, check the ID is unique.
+  if (BehaviorValue != Module::Require) {
+    Assert1(SeenIDs.insert(ID),
+            "module flag identifiers must be unique (or of 'require' type)",
+            ID);
+  }
+
+  // If this is a "requires" flag, sanity check the value.
+  if (BehaviorValue == Module::Require) {
+    // The value should itself be an MDNode with two operands, a flag ID (an
+    // MDString), and a value.
+    MDNode *Value = dyn_cast<MDNode>(Op->getOperand(2));
+    Assert1(Value && Value->getNumOperands() == 2,
+            "invalid value for 'require' module flag (expected metadata pair)",
+            Op->getOperand(2));
+    Assert1(isa<MDString>(Value->getOperand(0)),
+            ("invalid value for 'require' module flag "
+             "(first value operand should be a string)"),
+            Value->getOperand(0));
+  }
+}
+
 // VerifyParameterAttrs - Check the given attributes for an argument or return
 // value of the specified type.  The value V is printed in error messages.
 void Verifier::VerifyParameterAttrs(Attribute Attrs, Type *Ty,

test/Verifier/module-flags-1.ll

@@ -0,0 +1,37 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+; Check that module flags are structurally correct.
+;
+; CHECK: incorrect number of operands in module flag
+; CHECK: metadata !0
+!0 = metadata !{ i32 1 }
+; CHECK: invalid behavior operand in module flag (expected constant integer)
+; CHECK: metadata !"foo"
+!1 = metadata !{ metadata !"foo", metadata !"foo", i32 42 }
+; CHECK: invalid behavior operand in module flag (unexpected constant)
+; CHECK: i32 999
+!2 = metadata !{ i32 999, metadata !"foo", i32 43 }
+; CHECK: invalid ID operand in module flag (expected metadata string)
+; CHECK: i32 1
+!3 = metadata !{ i32 1, i32 1, i32 44 }
+; CHECK: invalid value for 'require' module flag (expected metadata pair)
+; CHECK: i32 45
+!4 = metadata !{ i32 3, metadata !"bla", i32 45 }
+; CHECK: invalid value for 'require' module flag (expected metadata pair)
+; CHECK: metadata !
+!5 = metadata !{ i32 3, metadata !"bla", metadata !{ i32 46 } }
+; CHECK: invalid value for 'require' module flag (first value operand should be a string)
+; CHECK: i32 47
+!6 = metadata !{ i32 3, metadata !"bla", metadata !{ i32 47, i32 48 } }
+
+; Check that module flags only have unique IDs.
+;
+; CHECK: module flag identifiers must be unique (or of 'require' type)
+!7 = metadata !{ i32 1, metadata !"foo", i32 49 }
+!8 = metadata !{ i32 2, metadata !"foo", i32 50 }
+; CHECK-NOT: module flag identifiers must be unique
+!9 = metadata !{ i32 2, metadata !"bar", i32 51 }
+!10 = metadata !{ i32 3, metadata !"bar", i32 51 }
+
+!llvm.module.flags = !{
+  !0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10 }