[WebAssembly] Add SIMD integer abs builtins

[tlively]

Summary

Since the conditional operator cannot be used with vector conditions
in C, we need a builtin to be able to express this operation in C
source.

clang/include/clang/Basic/BuiltinsWebAssembly.def

 TARGET_BUILTIN(__builtin_wasm_add_saturate_s_i16x8, "V8sV8sV8s", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_add_saturate_u_i16x8, "V8sV8sV8s", "nc", "simd128")
 
 TARGET_BUILTIN(__builtin_wasm_sub_saturate_s_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_sub_saturate_u_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_sub_saturate_s_i16x8, "V8sV8sV8s", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_sub_saturate_u_i16x8, "V8sV8sV8s", "nc", "simd128")
 
+TARGET_BUILTIN(__builtin_wasm_abs_i8x16, "V16cV16c", "nc", "simd128")
+TARGET_BUILTIN(__builtin_wasm_abs_i16x8, "V8sV8s", "nc", "simd128")
+TARGET_BUILTIN(__builtin_wasm_abs_i32x4, "V4iV4i", "nc", "simd128")
+
 TARGET_BUILTIN(__builtin_wasm_min_s_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_min_u_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_max_s_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_max_u_i8x16, "V16cV16cV16c", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_min_s_i16x8, "V8sV8sV8s", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_min_u_i16x8, "V8sV8sV8s", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_max_s_i16x8, "V8sV8sV8s", "nc", "simd128")
 TARGET_BUILTIN(__builtin_wasm_max_u_i16x8, "V8sV8sV8s", "nc", "simd128")

clang/lib/CodeGen/CGBuiltin.cpp

case WebAssembly::BI__builtin_wasm_sub_saturate_u_i16x8: {
     default:
       llvm_unreachable("unexpected builtin ID");
     }
     Value *LHS = EmitScalarExpr(E->getArg(0));
     Value *RHS = EmitScalarExpr(E->getArg(1));
     Function *Callee = CGM.getIntrinsic(IntNo, ConvertType(E->getType()));
     return Builder.CreateCall(Callee, {LHS, RHS});
   }
+  case WebAssembly::BI__builtin_wasm_abs_i8x16:
+  case WebAssembly::BI__builtin_wasm_abs_i16x8:
+  case WebAssembly::BI__builtin_wasm_abs_i32x4: {
+    Value *Vec = EmitScalarExpr(E->getArg(0));
+    Value *Neg = Builder.CreateNeg(Vec, "neg");
+    Constant *Zero = llvm::Constant::getNullValue(Vec->getType());
+    Value *ICmp = Builder.CreateICmpSLT(Vec, Zero, "abscond");
+    return Builder.CreateSelect(ICmp, Neg, Vec, "abs");
+  }
   case WebAssembly::BI__builtin_wasm_min_s_i8x16:
   case WebAssembly::BI__builtin_wasm_min_u_i8x16:
   case WebAssembly::BI__builtin_wasm_max_s_i8x16:
   case WebAssembly::BI__builtin_wasm_max_u_i8x16:
   case WebAssembly::BI__builtin_wasm_min_s_i16x8:
   case WebAssembly::BI__builtin_wasm_min_u_i16x8:
   case WebAssembly::BI__builtin_wasm_max_s_i16x8:
   case WebAssembly::BI__builtin_wasm_max_u_i16x8:

clang/test/CodeGen/builtins-wasm.c

 
 i8x16 sub_saturate_u_i8x16(i8x16 x, i8x16 y) {
   return __builtin_wasm_sub_saturate_u_i8x16(x, y);
   // WEBASSEMBLY: call <16 x i8> @llvm.wasm.sub.saturate.unsigned.v16i8(
   // WEBASSEMBLY-SAME: <16 x i8> %x, <16 x i8> %y)
   // WEBASSEMBLY-NEXT: ret
 }
 
+i8x16 abs_i8x16(i8x16 v) {
+  return __builtin_wasm_abs_i8x16(v);
+  // WEBASSEMBLY: %neg = sub <16 x i8> zeroinitializer, %v
+  // WEBASSEMBLY: %abscond = icmp slt <16 x i8> %v, zeroinitializer
+  // WEBASSEMBLY: %abs = select <16 x i1> %abscond, <16 x i8> %neg, <16 x i8> %v
+  // WEBASSEMBLY: ret <16 x i8> %abs
+}
+
+i16x8 abs_i16x8(i16x8 v) {
+  return __builtin_wasm_abs_i16x8(v);
+  // WEBASSEMBLY: %neg = sub <8 x i16> zeroinitializer, %v
+  // WEBASSEMBLY: %abscond = icmp slt <8 x i16> %v, zeroinitializer
+  // WEBASSEMBLY: %abs = select <8 x i1> %abscond, <8 x i16> %neg, <8 x i16> %v
+  // WEBASSEMBLY: ret <8 x i16> %abs
+}
+
+i32x4 abs_i32x4(i32x4 v) {
+  return __builtin_wasm_abs_i32x4(v);
+  // WEBASSEMBLY: %neg = sub <4 x i32> zeroinitializer, %v
+  // WEBASSEMBLY: %abscond = icmp slt <4 x i32> %v, zeroinitializer
+  // WEBASSEMBLY: %abs = select <4 x i1> %abscond, <4 x i32> %neg, <4 x i32> %v
+  // WEBASSEMBLY: ret <4 x i32> %abs
+}
+
 i8x16 min_s_i8x16(i8x16 x, i8x16 y) {
   return __builtin_wasm_min_s_i8x16(x, y);
   // WEBASSEMBLY: %0 = icmp slt <16 x i8> %x, %y
   // WEBASSEMBLY-NEXT: %1 = select <16 x i1> %0, <16 x i8> %x, <16 x i8> %y
   // WEBASSEMBLY-NEXT: ret <16 x i8> %1
 }
 
 i8x16 min_u_i8x16(i8x16 x, i8x16 y) {