[vm/compiler] Check BoxInt64 overflow via the overflow flag on ARM64.

This saves one instruction for every BoxInt64 overflow check, reducing
the instructions size for Flutter benchmarks by between 0.26% and 1.03%
(0.26% for Flutter Gallery).

Also add OVERFLOW and NO_OVERFLOW condition aliases to arm and arm64.

Change-Id: I82990419b448f21a22ea2cc7a15a9497d3275943
Cq-Do-Not-Cancel-Tryjobs: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/145860
Commit-Queue: Aske Simon Christensen <askesc@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

runtime/platform/globals.h

@@ -679,6 +679,9 @@ inline D bit_copy(const S& source) {
 #define PATH_MAX MAX_PATH
 #endif
 
+// Undefine math.h definition which clashes with our condition names.
+#undef OVERFLOW
+
 }  // namespace dart
 
 #endif  // RUNTIME_PLATFORM_GLOBALS_H_

runtime/vm/compiler/backend/il_arm64.cc

@@ -3984,10 +3984,11 @@ void BoxInt64Instr::EmitNativeCode(FlowGraphCompiler* compiler) {
     return;
   }
   ASSERT(kSmiTag == 0);
-  __ LslImmediate(out, in, kSmiTagSize);
+  __ adds(out, in, compiler::Operand(in));  // SmiTag
   compiler::Label done;
-  __ cmp(in, compiler::Operand(out, ASR, kSmiTagSize));
-  __ b(&done, EQ);
+  // If the value doesn't fit in a smi, the tagging changes the sign,
+  // which causes the overflow flag to be set.
+  __ b(&done, NO_OVERFLOW);
 
   Register temp = locs()->temp(0).reg();
 

runtime/vm/compiler/backend/il_x64.cc

@@ -4194,6 +4194,8 @@ void BoxInt64Instr::EmitNativeCode(FlowGraphCompiler* compiler) {
   if (!ValueFitsSmi()) {
     const Register temp = locs()->temp(0).reg();
     compiler::Label done;
+    // If the value doesn't fit in a smi, the tagging changes the sign,
+    // which causes the overflow flag to be set.
     __ j(NO_OVERFLOW, &done);
     BoxAllocationSlowPath::Allocate(compiler, this, compiler->mint_class(), out,
                                     temp);

runtime/vm/constants_arm.h

@@ -524,6 +524,8 @@ enum Condition {
   UNSIGNED_LESS_EQUAL = LS,
   UNSIGNED_GREATER = HI,
   UNSIGNED_GREATER_EQUAL = CS,
+  OVERFLOW = VS,
+  NO_OVERFLOW = VC,
 
   kInvalidCondition = 16
 };

runtime/vm/constants_arm64.h

@@ -374,6 +374,8 @@ enum Condition {
   UNSIGNED_LESS_EQUAL = LS,
   UNSIGNED_GREATER = HI,
   UNSIGNED_GREATER_EQUAL = CS,
+  OVERFLOW = VS,
+  NO_OVERFLOW = VC,
 
   kInvalidCondition = 16
 };

runtime/vm/globals.h

@@ -17,9 +17,6 @@
 #undef near
 #endif  // defined(_WIN32)
 
-// The following #defines are invalidated.
-#undef OVERFLOW  // From math.h conflicts in constants_ia32.h
-
 namespace dart {
 // Smi value range is from -(2^N) to (2^N)-1.
 // N=30 (32-bit build) or N=62 (64-bit build).