riscv64: Implemented StringEquals intrinsic

Bug: 283082089

Test: art/test/testrunner/testrunner.py --target --64 --ndebug --no-image --jit-on-first-use

Change-Id: Ifb4076d7f12cbad174049995980f0f08db41357a
Signed-off-by: denis.tomashev <denis.tomashev@syntacore.com>

2 files changed, 116 insertions, 1 deletions

diff --git a/compiler/optimizing/code_generator_riscv64.h b/compiler/optimizing/code_generator_riscv64.h
index 653e83dd57..4a80b17c28 100644
--- a/compiler/optimizing/code_generator_riscv64.h
+++ b/compiler/optimizing/code_generator_riscv64.h
@@ -72,7 +72,6 @@ static constexpr int32_t kFClassNaNMinValue = 0x100;
   V(FP16Min)                                    \
   V(FP16Max)                                    \
   V(StringCompareTo)                            \
-  V(StringEquals)                               \
   V(StringGetCharsNoCheck)                      \
   V(StringStringIndexOf)                        \
   V(StringStringIndexOfAfter)                   \
diff --git a/compiler/optimizing/intrinsics_riscv64.cc b/compiler/optimizing/intrinsics_riscv64.cc
index d5bcf1a7ae..12eec101b7 100644
--- a/compiler/optimizing/intrinsics_riscv64.cc
+++ b/compiler/optimizing/intrinsics_riscv64.cc
@@ -1073,6 +1073,122 @@ static void EmitLoadReserved(Riscv64Assembler* assembler,
   }
 }
 
+void IntrinsicLocationsBuilderRISCV64::VisitStringEquals(HInvoke* invoke) {
+  LocationSummary* locations =
+      new (allocator_) LocationSummary(invoke, LocationSummary::kNoCall, kIntrinsified);
+  locations->SetInAt(0, Location::RequiresRegister());
+  locations->SetInAt(1, Location::RequiresRegister());
+  locations->AddTemp(Location::RequiresRegister());
+  // TODO: If the String.equals() is used only for an immediately following HIf, we can
+  // mark it as emitted-at-use-site and emit branches directly to the appropriate blocks.
+  // Then we shall need an extra temporary register instead of the output register.
+  locations->SetOut(Location::RequiresRegister(), Location::kOutputOverlap);
+}
+
+void IntrinsicCodeGeneratorRISCV64::VisitStringEquals(HInvoke* invoke) {
+  Riscv64Assembler* assembler = GetAssembler();
+  LocationSummary* locations = invoke->GetLocations();
+
+  // Get offsets of count, value, and class fields within a string object.
+  const int32_t count_offset = mirror::String::CountOffset().Int32Value();
+  const int32_t value_offset = mirror::String::ValueOffset().Int32Value();
+  const int32_t class_offset = mirror::Object::ClassOffset().Int32Value();
+
+  XRegister str = locations->InAt(0).AsRegister<XRegister>();
+  XRegister arg = locations->InAt(1).AsRegister<XRegister>();
+  XRegister out = locations->Out().AsRegister<XRegister>();
+
+  ScratchRegisterScope srs(assembler);
+  XRegister temp = srs.AllocateXRegister();
+  XRegister temp1 = locations->GetTemp(0).AsRegister<XRegister>();
+
+  Riscv64Label loop;
+  Riscv64Label end;
+  Riscv64Label return_true;
+  Riscv64Label return_false;
+
+  DCHECK(!invoke->CanDoImplicitNullCheckOn(invoke->InputAt(0)));
+
+  StringEqualsOptimizations optimizations(invoke);
+  if (!optimizations.GetArgumentNotNull()) {
+    // Check if input is null, return false if it is.
+    __ Beqz(arg, &return_false);
+  }
+
+  // Reference equality check, return true if same reference.
+  __ Beq(str, arg, &return_true);
+
+  if (!optimizations.GetArgumentIsString()) {
+    // Instanceof check for the argument by comparing class fields.
+    // All string objects must have the same type since String cannot be subclassed.
+    // Receiver must be a string object, so its class field is equal to all strings' class fields.
+    // If the argument is a string object, its class field must be equal to receiver's class field.
+    //
+    // As the String class is expected to be non-movable, we can read the class
+    // field from String.equals' arguments without read barriers.
+    AssertNonMovableStringClass();
+    // /* HeapReference<Class> */ temp = str->klass_
+    __ Loadwu(temp, str, class_offset);
+    // /* HeapReference<Class> */ temp1 = arg->klass_
+    __ Loadwu(temp1, arg, class_offset);
+    // Also, because we use the previously loaded class references only in the
+    // following comparison, we don't need to unpoison them.
+    __ Bne(temp, temp1, &return_false);
+  }
+
+  // Load `count` fields of this and argument strings.
+  __ Loadwu(temp, str, count_offset);
+  __ Loadwu(temp1, arg, count_offset);
+  // Check if `count` fields are equal, return false if they're not.
+  // Also compares the compression style, if differs return false.
+  __ Bne(temp, temp1, &return_false);
+
+  // Assertions that must hold in order to compare strings 8 bytes at a time.
+  // Ok to do this because strings are zero-padded to kObjectAlignment.
+  DCHECK_ALIGNED(value_offset, 8);
+  static_assert(IsAligned<8>(kObjectAlignment), "String of odd length is not zero padded");
+
+  // Return true if both strings are empty. Even with string compression `count == 0` means empty.
+  static_assert(static_cast<uint32_t>(mirror::StringCompressionFlag::kCompressed) == 0u,
+                "Expecting 0=compressed, 1=uncompressed");
+  __ Beqz(temp, &return_true);
+
+  if (mirror::kUseStringCompression) {
+    // For string compression, calculate the number of bytes to compare (not chars).
+    // This could in theory exceed INT32_MAX, so treat temp as unsigned.
+    __ Andi(temp1, temp, 1);     // Extract compression flag.
+    __ Srliw(temp, temp, 1u);    // Extract length.
+    __ Sllw(temp, temp, temp1);  // Calculate number of bytes to compare.
+  }
+
+  // Store offset of string value in preparation for comparison loop
+  __ Li(temp1, value_offset);
+
+  XRegister temp2 = srs.AllocateXRegister();
+  // Loop to compare strings 8 bytes at a time starting at the front of the string.
+  __ Bind(&loop);
+  __ Add(out, str, temp1);
+  __ Ld(out, out, 0);
+  __ Add(temp2, arg, temp1);
+  __ Ld(temp2, temp2, 0);
+  __ Addi(temp1, temp1, sizeof(uint64_t));
+  __ Bne(out, temp2, &return_false);
+  // With string compression, we have compared 8 bytes, otherwise 4 chars.
+  __ Addi(temp, temp, mirror::kUseStringCompression ? -8 : -4);
+  __ Bgt(temp, Zero, &loop);
+
+  // Return true and exit the function.
+  // If loop does not result in returning false, we return true.
+  __ Bind(&return_true);
+  __ Li(out, 1);
+  __ J(&end);
+
+  // Return false and exit the function.
+  __ Bind(&return_false);
+  __ Li(out, 0);
+  __ Bind(&end);
+}
+
 static void EmitStoreConditional(Riscv64Assembler* assembler,
                                  DataType::Type type,
                                  XRegister ptr,