[libFuzzer] Use OptForFuzzing attribute with -fsanitize=fuzzer.

Summary:
Disables certain CMP optimizations to improve fuzzing signal under -O1
and -O2.

Switches all fuzzer tests to -O2 except for a few leak tests where the
leak is optimized out under -O2.

Reviewers: kcc, vitalybuka

Reviewed By: vitalybuka

Subscribers: cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D44798

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@328384 91177308-0d34-0410-b5e6-96231b3b80d8

test/fuzzer/SimpleCmpTest.cpp

@@ -17,15 +17,15 @@ bool PrintOnce(int Line) {
 }
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
-  if (Size != 22) return 0;
+  if (Size != 24) return 0;
   uint64_t x = 0;
   int64_t  y = 0;
   int32_t z = 0;
-  uint16_t a = 0;
+  uint32_t a = 0;
   memcpy(&x, Data, 8);  // 8
   memcpy(&y, Data + 8, 8);  // 16
   memcpy(&z, Data + 16, sizeof(z));  // 20
-  memcpy(&a, Data + 20, sizeof(a));  // 22
+  memcpy(&a, Data + 20, sizeof(a));  // 24
   const bool k32bit = sizeof(void*) == 4;
 
   if ((k32bit || x > 1234567890) && PrintOnce(__LINE__) &&

test/fuzzer/SwapCmpTest.cpp

@@ -11,22 +11,22 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   if (Size < 14) return 0;
   uint64_t x = 0;
   uint32_t y = 0;
-  uint16_t z = 0;
+  uint32_t z = 0;
   memcpy(&x, Data, sizeof(x));
   memcpy(&y, Data + Size / 2, sizeof(y));
   memcpy(&z, Data + Size - sizeof(z), sizeof(z));
 
   x = __builtin_bswap64(x);
   y = __builtin_bswap32(y);
-  z = __builtin_bswap16(z);
+  z = __builtin_bswap32(z);
   const bool k32bit = sizeof(void*) == 4;
 
   if ((k32bit || x == 0x46555A5A5A5A5546ULL) &&
       z == 0x4F4B &&
       y == 0x66757A7A &&
       true
       ) {
-    if (Data[Size - 3] == 'z') {
+    if (Data[Size - 5] == 'z') {
       fprintf(stderr, "BINGO; Found the target\n");
       exit(1);
     }

test/fuzzer/fuzzer-leak.test

@@ -1,6 +1,9 @@
 REQUIRES: lsan
-RUN: %cpp_compiler %S/LeakTest.cpp -o %t-LeakTest
-RUN: %cpp_compiler %S/ThreadedLeakTest.cpp -o %t-ThreadedLeakTest
+
+// Avoid optimizing since it causes these leaks to go away.
+RUN: %cpp_compiler -O0 %S/LeakTest.cpp -o %t-LeakTest
+RUN: %cpp_compiler -O0 %S/ThreadedLeakTest.cpp -o %t-ThreadedLeakTest
+
 RUN: %cpp_compiler %S/LeakTimeoutTest.cpp -o %t-LeakTimeoutTest
 
 RUN: rm -rf %t-corpus && mkdir -p %t-corpus

test/fuzzer/lit.cfg

@@ -64,7 +64,7 @@ def generate_compiler_cmd(is_cpp=True, fuzzer_enabled=True):
   sanitizers_cmd = ('-fsanitize=%s' % ','.join(sanitizers))
   isysroot_cmd = config.osx_sysroot_flag if config.osx_sysroot_flag else ''
   include_cmd = '-I%s' % libfuzzer_src_root
-  return '%s %s %s -gline-tables-only %s %s %s' % (
+  return '%s %s %s -O2 -gline-tables-only %s %s %s' % (
       compiler_cmd, std_cmd, link_cmd, isysroot_cmd, sanitizers_cmd, include_cmd)
 
 config.substitutions.append(('%cpp_compiler',

test/fuzzer/trace-malloc-threaded.test

@@ -2,7 +2,9 @@
 // printing a stack trace repeatedly
 UNSUPPORTED: darwin
 
-RUN: %cpp_compiler %S/TraceMallocThreadedTest.cpp -o %t-TraceMallocThreadedTest
+// Avoid optimizing since it causes the malloc to go away.
+RUN: %cpp_compiler -O0 %S/TraceMallocThreadedTest.cpp -o \
+RUN:   %t-TraceMallocThreadedTest
 
 RUN: %t-TraceMallocThreadedTest -trace_malloc=2 -runs=1 2>&1 | FileCheck %s
 CHECK: {{MALLOC\[[0-9]+] +0x[0-9]+ 5639}}