[codegen] Add FP returns to code stub linkage

- Adds kFPReturnRegister0 for all platforms.
- Reworks linkage.cc to assign return registers to the proper
  register type, using the new FP return register.

Bug: v8:10070

Change-Id: I5c876d248de9b825a1c80847ab134881dcda6f04
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2107510Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67183}

src/codegen/arm/register-arm.h

@@ -351,6 +351,8 @@ constexpr Register kWasmCompileLazyFuncIndexRegister = r4;
 constexpr Register cp = r7;              // JavaScript context pointer.
 constexpr Register kRootRegister = r10;  // Roots array pointer.
 
+constexpr DoubleRegister kFPReturnRegister0 = d0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/arm64/register-arm64.h

@@ -694,6 +694,8 @@ constexpr Register kRuntimeCallArgvRegister = x11;
 constexpr Register kWasmInstanceRegister = x7;
 constexpr Register kWasmCompileLazyFuncIndexRegister = x8;
 
+constexpr DoubleRegister kFPReturnRegister0 = d0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/ia32/register-ia32.h

@@ -159,6 +159,8 @@ constexpr Register kRootRegister = ebx;
 // TODO(860429): Remove remaining poisoning infrastructure on ia32.
 constexpr Register kSpeculationPoisonRegister = no_reg;
 
+constexpr DoubleRegister kFPReturnRegister0 = xmm1;  // xmm0 isn't allocatable.
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/mips/register-mips.h

@@ -376,6 +376,8 @@ constexpr Register kRuntimeCallArgvRegister = a2;
 constexpr Register kWasmInstanceRegister = a0;
 constexpr Register kWasmCompileLazyFuncIndexRegister = t0;
 
+constexpr DoubleRegister kFPReturnRegister0 = f0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/mips64/register-mips64.h

@@ -383,6 +383,8 @@ constexpr Register kRuntimeCallArgvRegister = a2;
 constexpr Register kWasmInstanceRegister = a0;
 constexpr Register kWasmCompileLazyFuncIndexRegister = t0;
 
+constexpr DoubleRegister kFPReturnRegister0 = f0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/ppc/register-ppc.h

@@ -306,6 +306,8 @@ constexpr Register kRuntimeCallArgvRegister = r5;
 constexpr Register kWasmInstanceRegister = r10;
 constexpr Register kWasmCompileLazyFuncIndexRegister = r15;
 
+constexpr DoubleRegister kFPReturnRegister0 = d0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/s390/register-s390.h

@@ -263,6 +263,8 @@ constexpr Register kRuntimeCallArgvRegister = r4;
 constexpr Register kWasmInstanceRegister = r6;
 constexpr Register kWasmCompileLazyFuncIndexRegister = r7;
 
+constexpr DoubleRegister kFPReturnRegister0 = d0;
+
 }  // namespace internal
 }  // namespace v8
 

src/codegen/x64/register-x64.h

@@ -217,6 +217,8 @@ constexpr Register kRootRegister = r13;  // callee save
 
 constexpr Register kOffHeapTrampolineRegister = kScratchRegister;
 
+constexpr DoubleRegister kFPReturnRegister0 = xmm0;
+
 }  // namespace internal
 }  // namespace v8
 

src/compiler/linkage.cc

@@ -21,6 +21,10 @@ inline LinkageLocation regloc(Register reg, MachineType type) {
   return LinkageLocation::ForRegister(reg.code(), type);
 }
 
+inline LinkageLocation regloc(DoubleRegister reg, MachineType type) {
+  return LinkageLocation::ForRegister(reg.code(), type);
+}
+
 }  // namespace
 
 
@@ -380,20 +384,33 @@ CallDescriptor* Linkage::GetStubCallDescriptor(
   LocationSignature::Builder locations(zone, return_count, parameter_count);
 
   // Add returns.
-  if (locations.return_count_ > 0) {
-    locations.AddReturn(regloc(kReturnRegister0, descriptor.GetReturnType(0)));
-  }
-  if (locations.return_count_ > 1) {
-    locations.AddReturn(regloc(kReturnRegister1, descriptor.GetReturnType(1)));
-  }
-  if (locations.return_count_ > 2) {
-    locations.AddReturn(regloc(kReturnRegister2, descriptor.GetReturnType(2)));
+  static constexpr Register return_registers[] = {
+      kReturnRegister0, kReturnRegister1, kReturnRegister2};
+  size_t num_returns = 0;
+  size_t num_fp_returns = 0;
+  for (size_t i = 0; i < locations.return_count_; i++) {
+    MachineType type = descriptor.GetReturnType(static_cast<int>(i));
+    if (IsFloatingPoint(type.representation())) {
+      DCHECK_LT(num_fp_returns, 1);  // Only 1 FP return is supported.
+      locations.AddReturn(regloc(kFPReturnRegister0, type));
+      num_fp_returns++;
+    } else {
+      DCHECK_LT(num_returns, arraysize(return_registers));
+      locations.AddReturn(regloc(return_registers[num_returns], type));
+      num_returns++;
+    }
   }
 
   // Add parameters in registers and on the stack.
   for (int i = 0; i < js_parameter_count; i++) {
     if (i < register_parameter_count) {
       // The first parameters go in registers.
+      // TODO(bbudge) Add floating point registers to the InterfaceDescriptor
+      // and use them for FP types. Currently, this works because on most
+      // platforms, all FP registers are available for use. On ia32, xmm0 is
+      // not allocatable and so we must work around that with platform-specific
+      // descriptors, adjusting the GP register set to avoid eax, which has
+      // register code 0.
       Register reg = descriptor.GetRegisterParameter(i);
       MachineType type = descriptor.GetParameterType(i);
       locations.AddParam(regloc(reg, type));

test/cctest/compiler/test-linkage.cc

@@ -104,6 +104,7 @@ TEST(TestLinkageRuntimeCall) {
 
 
 TEST(TestLinkageStubCall) {
+  // TODO(bbudge) Add tests for FP registers.
   Isolate* isolate = CcTest::InitIsolateOnce();
   Zone zone(isolate->allocator(), ZONE_NAME);
   Callable callable = Builtins::CallableFor(isolate, Builtins::kToNumber);