ARM64: optimize call immediate

src/arm64/assembler-arm64-inl.h

Index: src/arm64/assembler-arm64-inl.h
diff --git a/src/arm64/assembler-arm64-inl.h b/src/arm64/assembler-arm64-inl.h
index c509e05a5b7f7a3d4b43cda189b91980b6681e6f..0b58b08a7adecba84ef3c811350dd3f75d470558 100644
--- a/src/arm64/assembler-arm64-inl.h
+++ b/src/arm64/assembler-arm64-inl.h
@@ -589,30 +589,34 @@ Address Assembler::return_address_from_call_start(Address pc) {
   // sequences:
   //
   // Without relocation:
-  //  movz  ip0, #(target & 0x000000000000ffff)
-  //  movk  ip0, #(target & 0x00000000ffff0000)
-  //  movk  ip0, #(target & 0x0000ffff00000000)
-  //  movk  ip0, #(target & 0xffff000000000000)
-  //  blr   ip0
+  //  movz temp
+  //  [movk temp] (up to 2 instructions).
+  //  blr   temp
   //
   // With relocation:
-  //  ldr   ip0, =target
-  //  blr   ip0
+  //  ldr   temp, =target
+  //  blr   temp
   //
   // The return address is immediately after the blr instruction in both cases,
   // so it can be found by adding the call size to the address at the start of
   // the call sequence.
-  STATIC_ASSERT(Assembler::kCallSizeWithoutRelocation == 5 * kInstructionSize);
   STATIC_ASSERT(Assembler::kCallSizeWithRelocation == 2 * kInstructionSize);
 
   Instruction* instr = reinterpret_cast<Instruction*>(pc);
   if (instr->IsMovz()) {
+    int movk_count;
+    if (instr->following(1)->IsMovk()) {
+      if (instr->following(2)->IsMovk()) {
+        movk_count = 2;
+      } else {
+        movk_count = 1;
+      }
+    } else {
+      movk_count = 0;
+    }
     // Verify the instruction sequence.
-    ASSERT(instr->following(1)->IsMovk());
-    ASSERT(instr->following(2)->IsMovk());
-    ASSERT(instr->following(3)->IsMovk());
-    ASSERT(instr->following(4)->IsBranchAndLinkToRegister());
-    return pc + Assembler::kCallSizeWithoutRelocation;
+    ASSERT(instr->following(movk_count + 1)->IsBranchAndLinkToRegister());
+    return pc + (movk_count + 2) * kInstructionSize;
   } else {
     // Verify the instruction sequence.
     ASSERT(instr->IsLdrLiteralX());