Improve build times for debug builds (#1859)

* Rename simdjson_really_inline -> simdjson_inline

I want to change the simdjson_really_inline macro to sometimes not force
inlining. After that upcoming change, the name simdjson_really_inline
will no longer makes sense.

Rename simdjson_really_inline to simdjson_inline. This patch should not
change semantics; simdjson_inline still forces inlining as before.

Some functions still need to be really inlined for ABI reasons.
(GCC's -Wpsabi complains otherwise.) Leave those functions marked as
simdjson_really_inline.

* Improve build times for debug builds

simdjson_inline is used for most simdjson functions. It forces inlining.
In unoptimized/debug builds, this can lead to a lot of machine code
being generated (especially with Address Sanitizer), causing slow
compilation.

Change simdjson_inline to force inlining only for optimized builds.

Sometimes, the programmer might want a slightly-optimized build and want
fast compilation (e.g. GCC's -Og mode). Allow simdjson users to define
the simdjson_inline macro themselves (e.g. on the command line:
-Dsimdjson_inline=inline) in cases where the default behavior is
undesired.

This patch reduced build times by over 75% for ondemand_object_tests.cpp
with GCC 9.4.0 and CMAKE_BUILD_TYPE=Debug on my AMD 5950X:

Before: 6.885 6.683 6.971 6.957 6.949 seconds (5 samples)
After:  1.492 1.551 1.494 1.490 1.531 seconds (5 samples)

src/westmere/dom_parser_implementation.cpp

@@ -11,17 +11,17 @@ namespace {
 using namespace simd;
 
 struct json_character_block {
-  static simdjson_really_inline json_character_block classify(const simd::simd8x64<uint8_t>& in);
+  static simdjson_inline json_character_block classify(const simd::simd8x64<uint8_t>& in);
 
-  simdjson_really_inline uint64_t whitespace() const noexcept { return _whitespace; }
-  simdjson_really_inline uint64_t op() const noexcept { return _op; }
-  simdjson_really_inline uint64_t scalar() const noexcept { return ~(op() | whitespace()); }
+  simdjson_inline uint64_t whitespace() const noexcept { return _whitespace; }
+  simdjson_inline uint64_t op() const noexcept { return _op; }
+  simdjson_inline uint64_t scalar() const noexcept { return ~(op() | whitespace()); }
 
   uint64_t _whitespace;
   uint64_t _op;
 };
 
-simdjson_really_inline json_character_block json_character_block::classify(const simd::simd8x64<uint8_t>& in) {
+simdjson_inline json_character_block json_character_block::classify(const simd::simd8x64<uint8_t>& in) {
   // These lookups rely on the fact that anything < 127 will match the lower 4 bits, which is why
   // we can't use the generic lookup_16.
   auto whitespace_table = simd8<uint8_t>::repeat_16(' ', 100, 100, 100, 17, 100, 113, 2, 100, '\t', '\n', 112, 100, '\r', 100, 100);
@@ -80,11 +80,11 @@ simdjson_really_inline json_character_block json_character_block::classify(const
     return { whitespace, op };
 }
 
-simdjson_really_inline bool is_ascii(const simd8x64<uint8_t>& input) {
+simdjson_inline bool is_ascii(const simd8x64<uint8_t>& input) {
   return input.reduce_or().is_ascii();
 }
 
-simdjson_unused simdjson_really_inline simd8<bool> must_be_continuation(const simd8<uint8_t> prev1, const simd8<uint8_t> prev2, const simd8<uint8_t> prev3) {
+simdjson_unused simdjson_inline simd8<bool> must_be_continuation(const simd8<uint8_t> prev1, const simd8<uint8_t> prev2, const simd8<uint8_t> prev3) {
   simd8<uint8_t> is_second_byte = prev1.saturating_sub(0xc0u-1); // Only 11______ will be > 0
   simd8<uint8_t> is_third_byte  = prev2.saturating_sub(0xe0u-1); // Only 111_____ will be > 0
   simd8<uint8_t> is_fourth_byte = prev3.saturating_sub(0xf0u-1); // Only 1111____ will be > 0
@@ -92,7 +92,7 @@ simdjson_unused simdjson_really_inline simd8<bool> must_be_continuation(const si
   return simd8<int8_t>(is_second_byte | is_third_byte | is_fourth_byte) > int8_t(0);
 }
 
-simdjson_really_inline simd8<bool> must_be_2_3_continuation(const simd8<uint8_t> prev2, const simd8<uint8_t> prev3) {
+simdjson_inline simd8<bool> must_be_2_3_continuation(const simd8<uint8_t> prev2, const simd8<uint8_t> prev3) {
   simd8<uint8_t> is_third_byte  = prev2.saturating_sub(0xe0u-1); // Only 111_____ will be > 0
   simd8<uint8_t> is_fourth_byte = prev3.saturating_sub(0xf0u-1); // Only 1111____ will be > 0
   // Caller requires a bool (all 1's). All values resulting from the subtraction will be <= 64, so signed comparison is fine.
@@ -122,7 +122,7 @@ namespace SIMDJSON_IMPLEMENTATION {
 namespace {
 namespace stage1 {
 
-simdjson_really_inline uint64_t json_string_scanner::find_escaped(uint64_t backslash) {
+simdjson_inline uint64_t json_string_scanner::find_escaped(uint64_t backslash) {
   if (!backslash) { uint64_t escaped = prev_escaped; prev_escaped = 0; return escaped; }
   return find_escaped_branchless(backslash);
 }