Arm64: Ensure that csp is always aligned to 16 byte values even if jssp is not.

src/arm64/macro-assembler-arm64-inl.h

Index: src/arm64/macro-assembler-arm64-inl.h
diff --git a/src/arm64/macro-assembler-arm64-inl.h b/src/arm64/macro-assembler-arm64-inl.h
index 7c9258a9ca363aa13c7bcf9f1bb4511a52aa137f..d97e60391fef794bf9b485b17b02cccb7cee10ef 100644
--- a/src/arm64/macro-assembler-arm64-inl.h
+++ b/src/arm64/macro-assembler-arm64-inl.h
@@ -1246,29 +1246,56 @@ void MacroAssembler::Uxtw(const Register& rd, const Register& rn) {
 
 void MacroAssembler::BumpSystemStackPointer(const Operand& space) {
   ASSERT(!csp.Is(sp_));
-  // TODO(jbramley): Several callers rely on this not using scratch registers,
-  // so we use the assembler directly here. However, this means that large
-  // immediate values of 'space' cannot be handled cleanly. (Only 24-bits
-  // immediates or values of 'space' that can be encoded in one instruction are
-  // accepted.) Once we implement our flexible scratch register idea, we could
-  // greatly simplify this function.
-  InstructionAccurateScope scope(this);
-  if ((space.IsImmediate()) && !is_uint12(space.immediate())) {
-    // The subtract instruction supports a 12-bit immediate, shifted left by
-    // zero or 12 bits. So, in two instructions, we can subtract any immediate
-    // between zero and (1 << 24) - 1.
-    int64_t imm = space.immediate();
-    ASSERT(is_uint24(imm));
-
-    int64_t imm_top_12_bits = imm >> 12;
-    sub(csp, StackPointer(), imm_top_12_bits << 12);
-    imm -= imm_top_12_bits << 12;
-    if (imm > 0) {
-      sub(csp, csp, imm);
+  { InstructionAccurateScope scope(this);
+    if (!TmpList()->IsEmpty()) {
+      if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
+        UseScratchRegisterScope temps(this);
+        Register temp = temps.AcquireX();
+        sub(temp, StackPointer(), space);
+        bic(csp, temp, 0xf);
+      } else {
+        sub(csp, StackPointer(), space);
+      }
+    } else {
+      // TODO(jbramley): Several callers rely on this not using scratch
+      // registers, so we use the assembler directly here. However, this means
+      // that large immediate values of 'space' cannot be handled cleanly. (Only
+      // 24-bits immediates or values of 'space' that can be encoded in one
+      // instruction are accepted.) Once we implement our flexible scratch
+      // register idea, we could greatly simplify this function.
+      ASSERT(space.IsImmediate());
+      // Align to 16 bytes.
+      uint64_t imm = RoundUp(space.immediate(), 0x10);
+      ASSERT(is_uint24(imm));
+
+      Register source = StackPointer();
+      if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
+        bic(csp, source, 0xf);
+        source = csp;
+      }
+      if (!is_uint12(imm)) {
+        int64_t imm_top_12_bits = imm >> 12;
+        sub(csp, source, imm_top_12_bits << 12);
+        source = csp;
+        imm -= imm_top_12_bits << 12;
+      }
+      if (imm > 0) {
+        sub(csp, source, imm);
+      }
     }
-  } else {
-    sub(csp, StackPointer(), space);
   }
+  AssertStackConsistency();
+}
+
+
+void MacroAssembler::SyncSystemStackPointer() {
+  ASSERT(emit_debug_code());
+  ASSERT(!csp.Is(sp_));
+  if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
+    InstructionAccurateScope scope(this);
+    bic(csp, StackPointer(), 0xf);
+  }
+  AssertStackConsistency();
 }
 
 
@@ -1540,7 +1567,7 @@ void MacroAssembler::Drop(uint64_t count, uint64_t unit_size) {
     // It is safe to leave csp where it is when unwinding the JavaScript stack,
     // but if we keep it matching StackPointer, the simulator can detect memory
     // accesses in the now-free part of the stack.
-    Mov(csp, StackPointer());
+    SyncSystemStackPointer();
   }
 }
 
@@ -1562,7 +1589,7 @@ void MacroAssembler::Drop(const Register& count, uint64_t unit_size) {
     // It is safe to leave csp where it is when unwinding the JavaScript stack,
     // but if we keep it matching StackPointer, the simulator can detect memory
     // accesses in the now-free part of the stack.
-    Mov(csp, StackPointer());
+    SyncSystemStackPointer();
   }
 }
 
@@ -1584,7 +1611,7 @@ void MacroAssembler::DropBySMI(const Register& count_smi, uint64_t unit_size) {
     // It is safe to leave csp where it is when unwinding the JavaScript stack,
     // but if we keep it matching StackPointer, the simulator can detect memory
     // accesses in the now-free part of the stack.
-    Mov(csp, StackPointer());
+    SyncSystemStackPointer();
   }
 }