[WebAssembly] Remove WASM_FEATURE_PREFIX_REQUIRED (NFC) (llvm#113729)

This has not been emitted since

llvm@3f34e1b.

The corresponding proposed tool-conventions change:
WebAssembly/tool-conventions#236

Author: aheejin

lld/test/wasm/Inputs/require-feature-foo.yaml

@@ -9,9 +9,6 @@
 # RUN: yaml2obj %S/Inputs/use-feature-foo.yaml -o %t.used.o
 # RUN: wasm-ld --no-entry -o - %t1.o %t.used.o | obj2yaml | FileCheck %s --check-prefix USED
 
-# RUN: yaml2obj %S/Inputs/require-feature-foo.yaml -o %t.required.o
-# RUN: wasm-ld --no-entry -o - %t1.o %t.required.o | obj2yaml | FileCheck %s --check-prefix REQUIRED
-
 # RUN: yaml2obj %S/Inputs/disallow-feature-foo.yaml -o %t.disallowed.o
 # RUN: not wasm-ld --no-entry -o /dev/null %t1.o %t.disallowed.o 2>&1 | FileCheck %s --check-prefix DISALLOWED
 
@@ -24,7 +21,6 @@
 # give the expected results:
 #
 #     USED x USED => USED
-#     USED x REQUIRED => USED
 #     USED x DISALLOWED => Error
 #     USED x NONE => USED
 
@@ -73,13 +69,6 @@ Sections:
 # USED-NEXT:         Name:            foo
 # USED-NEXT: ...
 
-# REQUIRED:        - Type:            CUSTOM
-# REQUIRED:          Name:            target_features
-# REQUIRED-NEXT:     Features:
-# REQUIRED-NEXT:       - Prefix:          USED
-# REQUIRED-NEXT:         Name:            foo
-# REQUIRED-NEXT: ...
-
 # DISALLOWED: Target feature 'foo' used in {{.*}}target-feature-used.yaml.tmp1.o is disallowed by {{.*}}target-feature-used.yaml.tmp.disallowed.o. Use --no-check-features to suppress.{{$}}
 
 # DISALLOWED-NOCHECK:        - Type:            CUSTOM

lld/test/wasm/target-feature-required.yaml

@@ -572,7 +572,6 @@ void Writer::finalizeSections() {
 
 void Writer::populateTargetFeatures() {
   StringMap<std::string> used;
-  StringMap<std::string> required;
   StringMap<std::string> disallowed;
   SmallSet<std::string, 8> &allowed = out.targetFeaturesSec->features;
   bool tlsUsed = false;
@@ -599,18 +598,14 @@ void Writer::populateTargetFeatures() {
       goto done;
   }
 
-  // Find the sets of used, required, and disallowed features
+  // Find the sets of used and disallowed features
   for (ObjFile *file : ctx.objectFiles) {
     StringRef fileName(file->getName());
     for (auto &feature : file->getWasmObj()->getTargetFeatures()) {
       switch (feature.Prefix) {
       case WASM_FEATURE_PREFIX_USED:
         used.insert({feature.Name, std::string(fileName)});
         break;
-      case WASM_FEATURE_PREFIX_REQUIRED:
-        used.insert({feature.Name, std::string(fileName)});
-        required.insert({feature.Name, std::string(fileName)});
-        break;
       case WASM_FEATURE_PREFIX_DISALLOWED:
         disallowed.insert({feature.Name, std::string(fileName)});
         break;
@@ -662,7 +657,7 @@ void Writer::populateTargetFeatures() {
     }
   }
 
-  // Validate the required and disallowed constraints for each file
+  // Validate the disallowed constraints for each file
   for (ObjFile *file : ctx.objectFiles) {
     StringRef fileName(file->getName());
     SmallSet<std::string, 8> objectFeatures;
@@ -675,12 +670,6 @@ void Writer::populateTargetFeatures() {
               fileName + " is disallowed by " + disallowed[feature.Name] +
               ". Use --no-check-features to suppress.");
     }
-    for (const auto &feature : required.keys()) {
-      if (!objectFeatures.count(std::string(feature)))
-        error(Twine("Missing target feature '") + feature + "' in " + fileName +
-              ", required by " + required[feature] +
-              ". Use --no-check-features to suppress.");
-    }
   }
 
 done:

lld/test/wasm/target-feature-used.yaml

@@ -175,7 +175,6 @@ const unsigned WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND = 0x3;
 // Feature policy prefixes used in the custom "target_features" section
 enum : uint8_t {
   WASM_FEATURE_PREFIX_USED = '+',
-  WASM_FEATURE_PREFIX_REQUIRED = '=',
   WASM_FEATURE_PREFIX_DISALLOWED = '-',
 };
 

lld/wasm/Writer.cpp

@@ -999,7 +999,6 @@ Error WasmObjectFile::parseTargetFeaturesSection(ReadContext &Ctx) {
     Feature.Prefix = readUint8(Ctx);
     switch (Feature.Prefix) {
     case wasm::WASM_FEATURE_PREFIX_USED:
-    case wasm::WASM_FEATURE_PREFIX_REQUIRED:
     case wasm::WASM_FEATURE_PREFIX_DISALLOWED:
       break;
     default:

llvm/include/llvm/BinaryFormat/Wasm.h

@@ -342,7 +342,6 @@ void ScalarEnumerationTraits<WasmYAML::FeaturePolicyPrefix>::enumeration(
     IO &IO, WasmYAML::FeaturePolicyPrefix &Kind) {
 #define ECase(X) IO.enumCase(Kind, #X, wasm::WASM_FEATURE_PREFIX_##X);
   ECase(USED);
-  ECase(REQUIRED);
   ECase(DISALLOWED);
 #undef ECase
 }

llvm/lib/Object/WasmObjectFile.cpp

@@ -518,7 +518,6 @@ void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
 
     // Silently ignore invalid metadata
     if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
-        Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
       return;
 

llvm/lib/ObjectYAML/WasmYAML.cpp

@@ -8,8 +8,6 @@ Sections:
     Features:
       - Prefix:        USED
         Name:          "foo"
-      - Prefix:        REQUIRED
-        Name:          "bar"
       - Prefix:        DISALLOWED
         Name:          ""
 ...
@@ -19,7 +17,5 @@ Sections:
 # CHECK-NEXT:       Features:
 # CHECK-NEXT:         - Prefix:        USED
 # CHECK-NEXT:           Name:          foo
-# CHECK-NEXT:         - Prefix:        REQUIRED
-# CHECK-NEXT:           Name:          bar
 # CHECK-NEXT:         - Prefix:        DISALLOWED
 # CHECK-NEXT:           Name:          ''