Fix the C++11 runtime calls test.

Fix two related bugs:

1. Some inputs caused undefined behaviour when truncated to int8_t or int16_t.
2. The tests didn't properly perform sign extension on their return values
   before comparing with int32_t 'expected' values.

Also, update the simulator so that the tests would reliably fail without the
second fix.

Change-Id: If02f056d32d4515d55708804e2fb839a71d29e54

2 files changed, 22 insertions, 9 deletions

diff --git a/src/aarch64/simulator-aarch64.h b/src/aarch64/simulator-aarch64.h
index 84c81d8e..075a6061 100644
--- a/src/aarch64/simulator-aarch64.h
+++ b/src/aarch64/simulator-aarch64.h
@@ -1291,7 +1291,16 @@ class Simulator : public DecoderVisitor {
                            T value,
                            RegLogMode log_mode = LogRegWrites) {
     if (operand.IsCPURegister()) {
-      WriteCPURegister<T>(operand.GetCPURegister(), value, log_mode);
+      // Outside SIMD, registers are 64-bit or a subset of a 64-bit register. If
+      // the width of the value to write is smaller than 64 bits, the unused
+      // bits may contain unrelated values that the code following this write
+      // needs to handle gracefully.
+      // Here we fill the unused bits with a predefined pattern to catch issues
+      // early.
+      VIXL_ASSERT(operand.GetCPURegister().GetSizeInBits() <= 64);
+      uint64_t raw = 0xdeadda1adeadda1a;
+      memcpy(&raw, &value, sizeof(value));
+      WriteCPURegister(operand.GetCPURegister(), raw, log_mode);
     } else {
       VIXL_ASSERT(operand.IsMemOperand());
       Memory::Write(ComputeMemOperandAddress(operand.GetMemOperand()), value);
diff --git a/test/aarch64/test-assembler-aarch64.cc b/test/aarch64/test-assembler-aarch64.cc
index fb53213c..0a57ade6 100644
--- a/test/aarch64/test-assembler-aarch64.cc
+++ b/test/aarch64/test-assembler-aarch64.cc
@@ -28781,21 +28781,25 @@ TEST(runtime_calls) {
   for (size_t i = 0; i < sizeof(test_values) / sizeof(test_values[0]); ++i) {
     Label pass_int8, pass_uint8, pass_int16, pass_uint16;
     int x = test_values[i];
-    __ Mov(w0, static_cast<int8_t>(x));
+    __ Mov(w0, x);
     __ CallRuntime(test_int8_t);
-    __ Cmp(w0, static_cast<int8_t>(x));
+    __ Sxtb(w0, w0);
+    __ Cmp(w0, ExtractSignedBitfield32(7, 0, x));
     __ Cinc(x24, x24, ne);
-    __ Mov(w0, static_cast<uint8_t>(x));
+    __ Mov(w0, x);
     __ CallRuntime(test_uint8_t);
-    __ Cmp(w0, static_cast<uint8_t>(x));
+    __ Uxtb(w0, w0);
+    __ Cmp(w0, ExtractUnsignedBitfield32(7, 0, x));
     __ Cinc(x24, x24, ne);
-    __ Mov(w0, static_cast<int16_t>(x));
+    __ Mov(w0, x);
     __ CallRuntime(test_int16_t);
-    __ Cmp(w0, static_cast<int16_t>(x));
+    __ Sxth(w0, w0);
+    __ Cmp(w0, ExtractSignedBitfield32(15, 0, x));
     __ Cinc(x24, x24, ne);
-    __ Mov(w0, static_cast<uint16_t>(x));
+    __ Mov(w0, x);
     __ CallRuntime(test_uint16_t);
-    __ Cmp(w0, static_cast<uint16_t>(x));
+    __ Uxth(w0, w0);
+    __ Cmp(w0, ExtractUnsignedBitfield32(15, 0, x));
     __ Cinc(x24, x24, ne);
   }