Fixed a bug in the chaining of fixup position

The ARM and MIPS assemblers had a bug where they did not handle the last element
in the list of code positions correctly during the fixup of offsets for forward
jumps. This happened when the first instruction contained a forward jump to a
label, and that label was used in a forward jump later, too.

Unified the code for Assembler::next on ARM and MIPS while we were there.

Added test cases, even for ia32/x64, which seem to be correct, even I don't
fully understand why... %-}

BUG=v8:1644
Review URL: http://codereview.chromium.org/7786001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9063 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/assembler-arm.cc

@@ -692,11 +692,11 @@ void Assembler::bind(Label* L) {
 void Assembler::next(Label* L) {
   ASSERT(L->is_linked());
   int link = target_at(L->pos());
-  if (link > 0) {
-    L->link_to(link);
-  } else {
-    ASSERT(link == kEndOfChain);
+  if (link == kEndOfChain) {
     L->Unuse();
+  } else {
+    ASSERT(link >= 0);
+    L->link_to(link);
   }
 }
 

src/mips/assembler-mips.cc

@@ -780,10 +780,10 @@ void Assembler::bind(Label* L) {
 void Assembler::next(Label* L) {
   ASSERT(L->is_linked());
   int link = target_at(L->pos());
-  ASSERT(link > 0 || link == kEndOfChain);
   if (link == kEndOfChain) {
     L->Unuse();
-  } else if (link > 0) {
+  } else {
+    ASSERT(link >= 0);
     L->link_to(link);
   }
 }

test/cctest/test-assembler-arm.cc

@@ -1010,4 +1010,18 @@ TEST(11) {
   CHECK_EQ(0xffffffff, i.d);
 }
 
+
+TEST(12) {
+  // Test chaining of label usages within instructions (issue 1644).
+  InitializeVM();
+  v8::HandleScope scope;
+  Assembler assm(Isolate::Current(), NULL, 0);
+
+  Label target;
+  __ b(eq, &target);
+  __ b(ne, &target);
+  __ bind(&target);
+  __ nop();
+}
+
 #undef __

test/cctest/test-assembler-ia32.cc

@@ -394,4 +394,18 @@ TEST(AssemblerIa329) {
   CHECK_EQ(kNaN, f(OS::nan_value(), 1.1));
 }
 
+
+TEST(AssemblerIa3210) {
+  // Test chaining of label usages within instructions (issue 1644).
+  InitializeVM();
+  v8::HandleScope scope;
+  Assembler assm(Isolate::Current(), NULL, 0);
+
+  Label target;
+  __ j(equal, &target);
+  __ j(not_equal, &target);
+  __ bind(&target);
+  __ nop();
+}
+
 #undef __

test/cctest/test-assembler-mips.cc

@@ -1259,4 +1259,18 @@ TEST(MIPS14) {
   }
 }
 
+
+TEST(MIPS15) {
+  // Test chaining of label usages within instructions (issue 1644).
+  InitializeVM();
+  v8::HandleScope scope;
+  Assembler assm(Isolate::Current(), NULL, 0);
+
+  Label target;
+  __ beq(v0, v1, &target);
+  __ bne(v0, v1, &target);
+  __ bind(&target);
+  __ nop();
+}
+
 #undef __

test/cctest/test-assembler-x64.cc

@@ -46,6 +46,7 @@ using v8::internal::Operand;
 using v8::internal::byte;
 using v8::internal::greater;
 using v8::internal::less_equal;
+using v8::internal::equal;
 using v8::internal::not_equal;
 using v8::internal::r13;
 using v8::internal::r15;
@@ -345,4 +346,17 @@ TEST(OperandRegisterDependency) {
   }
 }
 
+
+TEST(AssemblerX64LabelChaining) {
+  // Test chaining of label usages within instructions (issue 1644).
+  v8::HandleScope scope;
+  Assembler assm(Isolate::Current(), NULL, 0);
+
+  Label target;
+  __ j(equal, &target);
+  __ j(not_equal, &target);
+  __ bind(&target);
+  __ nop();
+}
+
 #undef __