[instruction scheduler] deal with CSP/JSSP disparity on arm64.

This is preparation work to re-enable the scheduler: on arm64 some opcodes will
be neutral wrt the stack (JSSP) but will modify the underlying CSP. Identify
those opcode as such until JSSP is removed.

Bug: 
Change-Id: Iae633382c5ed38b01edaec896f2ce44d76931fc8
Reviewed-on: https://chromium-review.googlesource.com/568822Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Rodolph Perfetta <rodolph.perfetta@arm.com>
Cr-Commit-Position: refs/heads/master@{#46946}

src/compiler/arm64/instruction-scheduler-arm64.cc

@@ -93,7 +93,6 @@ int InstructionScheduler::GetTargetInstructionFlags(
     case kArm64Float64Sub:
     case kArm64Float64Mul:
     case kArm64Float64Div:
-    case kArm64Float64Mod:
     case kArm64Float64Max:
     case kArm64Float64Min:
     case kArm64Float64Abs:
@@ -295,6 +294,8 @@ int InstructionScheduler::GetTargetInstructionFlags(
     case kArm64Ldr:
       return kIsLoadOperation;
 
+    case kArm64Float64Mod:  // This opcode will call a C Function which can
+                            // alter CSP. TODO(arm64): Remove once JSSP is gone.
     case kArm64ClaimCSP:
     case kArm64ClaimJSSP:
     case kArm64PokeCSP:

src/compiler/instruction-scheduler.cc

@@ -240,9 +240,13 @@ int InstructionScheduler::GetInstructionFlags(const Instruction* instr) const {
     case kArchNop:
     case kArchFramePointer:
     case kArchParentFramePointer:
-    case kArchTruncateDoubleToI:
-    case kArchStackSlot:
+    case kArchStackSlot:  // Despite its name this opcode will produce a
+                          // reference to a frame slot, so it is not affected
+                          // by the arm64 dual stack issues mentioned below.
     case kArchComment:
+      return kNoOpcodeFlags;
+
+    case kArchTruncateDoubleToI:
     case kIeee754Float64Acos:
     case kIeee754Float64Acosh:
     case kIeee754Float64Asin:
@@ -264,7 +268,21 @@ int InstructionScheduler::GetInstructionFlags(const Instruction* instr) const {
     case kIeee754Float64Sinh:
     case kIeee754Float64Tan:
     case kIeee754Float64Tanh:
+#ifdef V8_TARGET_ARCH_ARM64
+      // This is an unfortunate effect of arm64 dual stack pointers:
+      //  * TruncateDoubleToI may call a stub, and the stub will push and pop
+      //    values onto the stack. Push updates both CSP and JSSP but pop only
+      //    restores JSSP.
+      //  * kIeee754XXX opcodes call a C Function and the call macro may update
+      //    CSP to meet alignment requirements but it will not bring back CSP to
+      //    its original value.
+      // Those opcode cannot be reordered with instructions with side effects
+      // such as Arm64ClaimCSP.
+      // TODO(arm64): remove when JSSP is gone.
+      return kHasSideEffect;
+#else
       return kNoOpcodeFlags;
+#endif
 
     case kArchStackPointer:
       // ArchStackPointer instruction loads the current stack pointer value and