[Liftoff] Implement reinterpretations

This adds support for i32.reinterpret/f32, i64.reinterpret/f64,
f32.reinterpret/i32, and f64.reinterpret/i64.
On x64, all operations are straight-forward. On ia32, conversions from
or to i64 are done via the stack.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: If5562caf7367726904c6e405ad4fc5436d21144e
Reviewed-on: https://chromium-review.googlesource.com/962224Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51920}

src/wasm/baseline/ia32/liftoff-assembler-ia32.h

@@ -696,6 +696,17 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
                                             LiftoffRegister dst,
                                             LiftoffRegister src) {
   switch (opcode) {
+    case kExprI32ReinterpretF32:
+      Movd(dst.gp(), src.fp());
+      return true;
+    case kExprI64ReinterpretF64:
+      // Push src to the stack.
+      sub(esp, Immediate(8));
+      movsd(Operand(esp, 0), src.fp());
+      // Pop to dst.
+      pop(dst.low_gp());
+      pop(dst.high_gp());
+      return true;
     case kExprF32SConvertI32:
       cvtsi2ss(dst.fp(), src.gp());
       return true;
@@ -708,6 +719,9 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
     case kExprF32ConvertF64:
       cvtsd2ss(dst.fp(), src.fp());
       return true;
+    case kExprF32ReinterpretI32:
+      Movd(dst.fp(), src.gp());
+      return true;
     case kExprF64SConvertI32:
       Cvtsi2sd(dst.fp(), src.gp());
       return true;
@@ -717,6 +731,14 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
     case kExprF64ConvertF32:
       cvtss2sd(dst.fp(), src.fp());
       return true;
+    case kExprF64ReinterpretI64:
+      // Push src to the stack.
+      push(src.high_gp());
+      push(src.low_gp());
+      // Pop to dst.
+      movsd(dst.fp(), Operand(esp, 0));
+      add(esp, Immediate(8));
+      return true;
     default:
       return false;
   }

src/wasm/baseline/liftoff-compiler.cc

@@ -625,6 +625,8 @@ class LiftoffCompiler {
         CASE_FLOAT_UNOP(F32Sqrt, F32, f32_sqrt)
         CASE_FLOAT_UNOP(F64Neg, F64, f64_neg)
         CASE_FLOAT_UNOP(F64Sqrt, F64, f64_sqrt)
+        CASE_TYPE_CONVERSION(I32ReinterpretF32, I32, F32, nullptr)
+        CASE_TYPE_CONVERSION(I64ReinterpretF64, I64, F64, nullptr)
         CASE_TYPE_CONVERSION(F32SConvertI32, F32, I32, nullptr)
         CASE_TYPE_CONVERSION(F32UConvertI32, F32, I32, nullptr)
         CASE_TYPE_CONVERSION(F32SConvertI64, F32, I64,
@@ -632,6 +634,7 @@ class LiftoffCompiler {
         CASE_TYPE_CONVERSION(F32UConvertI64, F32, I64,
                              &ExternalReference::wasm_uint64_to_float32)
         CASE_TYPE_CONVERSION(F32ConvertF64, F32, F64, nullptr)
+        CASE_TYPE_CONVERSION(F32ReinterpretI32, F32, I32, nullptr)
         CASE_TYPE_CONVERSION(F64SConvertI32, F64, I32, nullptr)
         CASE_TYPE_CONVERSION(F64UConvertI32, F64, I32, nullptr)
         CASE_TYPE_CONVERSION(F64SConvertI64, F64, I64,
@@ -639,6 +642,7 @@ class LiftoffCompiler {
         CASE_TYPE_CONVERSION(F64UConvertI64, F64, I64,
                              &ExternalReference::wasm_uint64_to_float64)
         CASE_TYPE_CONVERSION(F64ConvertF32, F64, F32, nullptr)
+        CASE_TYPE_CONVERSION(F64ReinterpretI64, F64, I64, nullptr)
       default:
         return unsupported(decoder, WasmOpcodes::OpcodeName(opcode));
     }

src/wasm/baseline/x64/liftoff-assembler-x64.h

@@ -643,6 +643,12 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
                                             LiftoffRegister dst,
                                             LiftoffRegister src) {
   switch (opcode) {
+    case kExprI32ReinterpretF32:
+      Movd(dst.gp(), src.fp());
+      return true;
+    case kExprI64ReinterpretF64:
+      Movq(dst.gp(), src.fp());
+      return true;
     case kExprF32SConvertI32:
       Cvtlsi2ss(dst.fp(), src.gp());
       return true;
@@ -659,6 +665,9 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
     case kExprF32ConvertF64:
       Cvtsd2ss(dst.fp(), src.fp());
       return true;
+    case kExprF32ReinterpretI32:
+      Movd(dst.fp(), src.gp());
+      return true;
     case kExprF64SConvertI32:
       Cvtlsi2sd(dst.fp(), src.gp());
       return true;
@@ -675,6 +684,9 @@ bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,
     case kExprF64ConvertF32:
       Cvtss2sd(dst.fp(), src.fp());
       return true;
+    case kExprF64ReinterpretI64:
+      Movq(dst.fp(), src.gp());
+      return true;
     default:
       UNREACHABLE();
   }