[compiler-rt] [windows] Add UNUSED attributes on variables/functions only used for 64 bit targets

[mstorsjo]

Summary

This fixes warnings when building for 32 bit targets.

Alternatively we could stick a few (void)var; in some 32-bit-only codepath.

[amccarth]

compiler-rt/lib/interception/interception_win.cpp

139

I suppose this is fine, but it seems most of these could be constexpr, which would obviate the need for the preprocessor macro.

[mstorsjo]

compiler-rt/lib/interception/interception_win.cpp

139

Hmm, making them constexpr doesn't seem to help to silence the warnings:

$ cat test.cpp
constexpr int unusedVar = 42;
void func() { }
$ clang -target x86_64-w64-mingw32 -c test.cpp -Wall
test.cpp:2:15: warning: unused variable 'unusedVar' [-Wunused-const-variable]
constexpr int unusedVar = 42;
              ^ 
1 warning generated.

(Same also goes for a MSVC triple.)

[mstorsjo]

Ping @amccarth, do you want to follow up on the discussion before I land this?

[amccarth]

In D91852#2460100, @mstorsjo wrote:

Ping @amccarth, do you want to follow up on the discussion before I land this?

Sorry about the delay -- holidays. Landing this without further discussion was fine by me.

compiler-rt/lib/interception/interception_win.cpp

 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
 namespace __interception {
 
 static const int kAddressLength = FIRST_32_SECOND_64(4, 8);
 static const int kJumpInstructionLength = 5;
 static const int kShortJumpInstructionLength = 2;
-static const int kIndirectJumpInstructionLength = 6;
+UNUSED static const int kIndirectJumpInstructionLength = 6;
 static const int kBranchLength =
     FIRST_32_SECOND_64(kJumpInstructionLength, kIndirectJumpInstructionLength);
 static const int kDirectBranchLength = kBranchLength + kAddressLength;
 
 static void InterceptionFailed() {
   // Do we have a good way to abort with an error message here?
   __debugbreak();
 }

 }
 
 static uptr GetMmapGranularity() {
   SYSTEM_INFO si;
   GetSystemInfo(&si);
   return si.dwAllocationGranularity;
 }
 
-static uptr RoundUpTo(uptr size, uptr boundary) {
+UNUSED static uptr RoundUpTo(uptr size, uptr boundary) {
   return (size + boundary - 1) & ~(boundary - 1);
 }
 
 // FIXME: internal_str* and internal_mem* functions should be moved from the
 // ASan sources into interception/.
 
 static size_t _strlen(const char *str) {
   const char* p = str;

 }
 
 struct TrampolineMemoryRegion {
   uptr content;
   uptr allocated_size;
   uptr max_size;
 };
 
-static const uptr kTrampolineScanLimitRange = 1 << 31;  // 2 gig
+UNUSED static const uptr kTrampolineScanLimitRange = 1 << 31;  // 2 gig
 static const int kMaxTrampolineRegion = 1024;
 static TrampolineMemoryRegion TrampolineRegions[kMaxTrampolineRegion];
 
 static void *AllocateTrampolineRegion(uptr image_address, size_t granularity) {
 #if SANITIZER_WINDOWS64
   uptr address = image_address;
   uptr scanned = 0;
   while (scanned < kTrampolineScanLimitRange) {