[WebAssembly] Add relaxed-simd feature

[ngzhian]

Summary

This currently only defines a constant, but it the future will be used
to gate builtins for experimenting and prototyping relaxed-simd proposal
(https://github.com/WebAssembly/relaxed-simd/).

[ngzhian]

I followed https://reviews.llvm.org/rGb7b9fdc114c1f9c788da914dac5c343277805446 for this, hope it's right, ptal Thomas.

[tlively]

Nice! Thanks for writing this :D Do you know what happens when you actually try to compile some code with -mrelaxed-simd? I'm concerned that it will throw an error because the "relaxed-simd" target feature has not yet been defined in the backend (specifically in WebAssembly.td and in WebAssemblySubtarget.{h,cpp}).

Edit: Here's the corresponding previous patch that added the target feature in the backend: https://reviews.llvm.org/D56501.

clang/lib/Basic/Targets/WebAssembly.cpp

105–107

I believe this should be above the SIMD128 case so that when RelaxedSIMD is enabled it falls through and marks SIMD128 as enabled as well.

[ngzhian]

Fix fallthrough, add feature to WebAssembly subtarget

[ngzhian]

In D110111#3013948, @tlively wrote:

Nice! Thanks for writing this :D Do you know what happens when you actually try to compile some code with -mrelaxed-simd? I'm concerned that it will throw an error because the "relaxed-simd" target feature has not yet been defined in the backend (specifically in WebAssembly.td and in WebAssemblySubtarget.{h,cpp}).

It output "'+relaxed-simd' is not a recognized feature for this target (ignoring feature)" but didn't fail compilation. I fixed it by adding to WebAssembly.td and WebAssemblySubtarget.h, thanks!

Edit: Here's the corresponding previous patch that added the target feature in the backend: https://reviews.llvm.org/D56501.

[tlively]

Great, thanks! I will take care of landing this.

clang/include/clang/Driver/Options.td

 def mbranch_protection_EQ : Joined<["-"], "mbranch-protection=">,
   HelpText<"Enforce targets of indirect branches and function returns">;
 
 def mharden_sls_EQ : Joined<["-"], "mharden-sls=">,
   HelpText<"Select straight-line speculation hardening scope">;
 
 def msimd128 : Flag<["-"], "msimd128">, Group<m_wasm_Features_Group>;
 def mno_simd128 : Flag<["-"], "mno-simd128">, Group<m_wasm_Features_Group>;
+def mrelaxed_simd : Flag<["-"], "mrelaxed-simd">, Group<m_wasm_Features_Group>;
+def mno_relaxed_simd : Flag<["-"], "mno-relaxed-simd">, Group<m_wasm_Features_Group>;
 def mnontrapping_fptoint : Flag<["-"], "mnontrapping-fptoint">, Group<m_wasm_Features_Group>;
 def mno_nontrapping_fptoint : Flag<["-"], "mno-nontrapping-fptoint">, Group<m_wasm_Features_Group>;
 def msign_ext : Flag<["-"], "msign-ext">, Group<m_wasm_Features_Group>;
 def mno_sign_ext : Flag<["-"], "mno-sign-ext">, Group<m_wasm_Features_Group>;
 def mexception_handing : Flag<["-"], "mexception-handling">, Group<m_wasm_Features_Group>;
 def mno_exception_handing : Flag<["-"], "mno-exception-handling">, Group<m_wasm_Features_Group>;
 def matomics : Flag<["-"], "matomics">, Group<m_wasm_Features_Group>;
 def mno_atomics : Flag<["-"], "mno-atomics">, Group<m_wasm_Features_Group>;

clang/lib/Basic/Targets/WebAssembly.h

 namespace targets {
 
 class LLVM_LIBRARY_VISIBILITY WebAssemblyTargetInfo : public TargetInfo {
   static const Builtin::Info BuiltinInfo[];
 
   enum SIMDEnum {
     NoSIMD,
     SIMD128,
+    RelaxedSIMD,
   } SIMDLevel = NoSIMD;
 
   bool HasNontrappingFPToInt = false;
   bool HasSignExt = false;
   bool HasExceptionHandling = false;
   bool HasBulkMemory = false;
   bool HasAtomics = false;
   bool HasMutableGlobals = false;

clang/lib/Basic/Targets/WebAssembly.cpp

bool WebAssemblyTargetInfo::setABI(const std::string &Name) {
 
   ABI = Name;
   return true;
 }
 
 bool WebAssemblyTargetInfo::hasFeature(StringRef Feature) const {
   return llvm::StringSwitch<bool>(Feature)
       .Case("simd128", SIMDLevel >= SIMD128)
+      .Case("relaxed-simd", SIMDLevel >= RelaxedSIMD)
       .Case("nontrapping-fptoint", HasNontrappingFPToInt)
       .Case("sign-ext", HasSignExt)
       .Case("exception-handling", HasExceptionHandling)
       .Case("bulk-memory", HasBulkMemory)
       .Case("atomics", HasAtomics)
       .Case("mutable-globals", HasMutableGlobals)
       .Case("multivalue", HasMultivalue)
       .Case("tail-call", HasTailCall)
void WebAssemblyTargetInfo::fillValidCPUList(
   Values.append(std::begin(ValidCPUNames), std::end(ValidCPUNames));
 }
 
 void WebAssemblyTargetInfo::getTargetDefines(const LangOptions &Opts,
                                              MacroBuilder &Builder) const {
   defineCPUMacros(Builder, "wasm", /*Tuning=*/false);
   if (SIMDLevel >= SIMD128)
     Builder.defineMacro("__wasm_simd128__");
+  if (SIMDLevel >= RelaxedSIMD)
+    Builder.defineMacro("__wasm_relaxed_simd__");
   if (HasNontrappingFPToInt)
     Builder.defineMacro("__wasm_nontrapping_fptoint__");
   if (HasSignExt)
     Builder.defineMacro("__wasm_sign_ext__");
   if (HasExceptionHandling)
     Builder.defineMacro("__wasm_exception_handling__");
   if (HasBulkMemory)
     Builder.defineMacro("__wasm_bulk_memory__");

 
 void WebAssemblyTargetInfo::setSIMDLevel(llvm::StringMap<bool> &Features,
                                          SIMDEnum Level, bool Enabled) {
   if (Enabled) {
     switch (Level) {
     case SIMD128:
       Features["simd128"] = true;
       LLVM_FALLTHROUGH;
+    case RelaxedSIMD:
+      Features["relaxed-simd"] = true;
+      LLVM_FALLTHROUGH;
     case NoSIMD:
       break;
     }
     return;
   }
 
   switch (Level) {
   case NoSIMD:
   case SIMD128:
     Features["simd128"] = false;
+    LLVM_FALLTHROUGH;
+  case RelaxedSIMD:
+    Features["relaxed-simd"] = false;
     break;
   }
 }
 
 void WebAssemblyTargetInfo::setFeatureEnabled(llvm::StringMap<bool> &Features,
                                               StringRef Name,
                                               bool Enabled) const {
   if (Name == "simd128")
     setSIMDLevel(Features, SIMD128, Enabled);
+  else if (Name == "relaxed-simd")
+    setSIMDLevel(Features, RelaxedSIMD, Enabled);
   else
     Features[Name] = Enabled;
 }
 
 bool WebAssemblyTargetInfo::initFeatureMap(
     llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags, StringRef CPU,
     const std::vector<std::string> &FeaturesVec) const {
   if (CPU == "bleeding-edge") {
for (const auto &Feature : Features) {
     if (Feature == "+simd128") {
       SIMDLevel = std::max(SIMDLevel, SIMD128);
       continue;
     }
     if (Feature == "-simd128") {
       SIMDLevel = std::min(SIMDLevel, SIMDEnum(SIMD128 - 1));
       continue;
     }
+    if (Feature == "+relaxed-simd") {
+      SIMDLevel = std::max(SIMDLevel, RelaxedSIMD);
+      continue;
+    }
+    if (Feature == "-relaxed-simd") {
+      SIMDLevel = std::min(SIMDLevel, SIMDEnum(RelaxedSIMD - 1));
+      continue;
+    }
     if (Feature == "+nontrapping-fptoint") {
       HasNontrappingFPToInt = true;
       continue;
     }
     if (Feature == "-nontrapping-fptoint") {
       HasNontrappingFPToInt = false;
       continue;
     }

clang/test/Preprocessor/wasm-target-features.c

 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -msimd128 \
 // RUN:   | FileCheck %s -check-prefix=SIMD128
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm64-unknown-unknown -msimd128 \
 // RUN:   | FileCheck %s -check-prefix=SIMD128
 //
 // SIMD128:#define __wasm_simd128__ 1{{$}}
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm32-unknown-unknown -mrelaxed-simd \
+// RUN:   | FileCheck %s -check-prefix=RELAXED-SIMD
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm64-unknown-unknown -mrelaxed-simd \
+// RUN:   | FileCheck %s -check-prefix=RELAXED-SIMD
+//
+// RELAXED-SIMD:#define __wasm_relaxed_simd__ 1{{$}}
+
+// RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mnontrapping-fptoint \
 // RUN:   | FileCheck %s -check-prefix=NONTRAPPING-FPTOINT
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm64-unknown-unknown -mnontrapping-fptoint \
 // RUN:   | FileCheck %s -check-prefix=NONTRAPPING-FPTOINT
 //
 // NONTRAPPING-FPTOINT:#define __wasm_nontrapping_fptoint__ 1{{$}}