From a27ec228d46ced2850cbbfcc88ca2947e05f248d Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mon, 24 Jun 2019 23:43:06 +0200
Subject: [PATCH] mimalloc: offer a build-time option to enable it

By defining `USE_MIMALLOC`, Git can now be compiled with that
nicely-fast and small allocator.

Note that we have to disable a couple `DEVELOPER` options to build
mimalloc's source code, as it makes heavy use of declarations after
statements, among other things that disagree with Git's conventions.

We even have to silence some GCC warnings in non-DEVELOPER mode. For
example, the `-Wno-array-bounds` flag is needed because in `-O2` builds,
trying to call `NtCurrentTeb()` (which `_mi_thread_id()` does on
Windows) causes the bogus warning about a system header, likely related
to https://sourceforge.net/p/mingw-w64/mailman/message/37674519/ and to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578:

C:/git-sdk-64-minimal/mingw64/include/psdk_inc/intrin-impl.h:838:1:
        error: array subscript 0 is outside array bounds of 'long long unsigned int[0]' [-Werror=array-bounds]
  838 | __buildreadseg(__readgsqword, unsigned __int64, "gs", "q")
      | ^~~~~~~~~~~~~~

Also: The `mimalloc` library uses C11-style atomics, therefore we must
require that standard when compiling with GCC if we want to use
`mimalloc` (instead of requiring "only" C99). This is what we do in the
CMake definition already, therefore this commit does not need to touch
`contrib/buildsystems/`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Makefile          | 37 +++++++++++++++++++++++++++++++++++++
 config.mak.dev    |  2 ++
 config.mak.uname  |  2 +-
 git-compat-util.h | 10 ++++++++++
 4 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 995afe21733af4..9617ae86807cc4 100644
--- a/Makefile
+++ b/Makefile
@@ -2124,6 +2124,43 @@ ifdef USE_NED_ALLOCATOR
 	OVERRIDE_STRDUP = YesPlease
 endif
 
+ifdef USE_MIMALLOC
+	MIMALLOC_OBJS = \
+		compat/mimalloc/alloc-aligned.o \
+		compat/mimalloc/alloc.o \
+		compat/mimalloc/arena.o \
+		compat/mimalloc/bitmap.o \
+		compat/mimalloc/heap.o \
+		compat/mimalloc/init.o \
+		compat/mimalloc/options.o \
+		compat/mimalloc/os.o \
+		compat/mimalloc/page.o \
+		compat/mimalloc/random.o \
+		compat/mimalloc/prim/windows/prim.o \
+		compat/mimalloc/segment.o \
+		compat/mimalloc/segment-cache.o \
+		compat/mimalloc/segment-map.o \
+		compat/mimalloc/stats.o
+
+	COMPAT_CFLAGS += -Icompat/mimalloc -DMI_DEBUG=0 -DUSE_MIMALLOC --std=gnu11
+	COMPAT_OBJS += $(MIMALLOC_OBJS)
+
+$(MIMALLOC_OBJS): COMPAT_CFLAGS += -DBANNED_H
+
+$(MIMALLOC_OBJS): COMPAT_CFLAGS += \
+	-Wno-attributes \
+	-Wno-unknown-pragmas \
+	-Wno-array-bounds
+
+ifdef DEVELOPER
+$(MIMALLOC_OBJS): COMPAT_CFLAGS += \
+	-Wno-pedantic \
+	-Wno-declaration-after-statement \
+	-Wno-old-style-definition \
+	-Wno-missing-prototypes
+endif
+endif
+
 ifdef OVERRIDE_STRDUP
 	COMPAT_CFLAGS += -DOVERRIDE_STRDUP
 	COMPAT_OBJS += compat/strdup.o
diff --git a/config.mak.dev b/config.mak.dev
index 0fd8cc4d355ebb..a5d6dd67dfd77e 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -22,8 +22,10 @@ endif
 
 ifneq ($(uname_S),FreeBSD)
 ifneq ($(or $(filter gcc6,$(COMPILER_FEATURES)),$(filter clang7,$(COMPILER_FEATURES))),)
+ifndef USE_MIMALLOC
 DEVELOPER_CFLAGS += -std=gnu99
 endif
+endif
 else
 # FreeBSD cannot limit to C99 because its system headers unconditionally
 # rely on C11 features.
diff --git a/config.mak.uname b/config.mak.uname
index 7fba3e595c5cd5..cdfb606f010ba4 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -494,7 +494,7 @@ endif
 	CC = compat/vcbuild/scripts/clink.pl
 	AR = compat/vcbuild/scripts/lib.pl
 	CFLAGS =
-	BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
+	BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE -MP -std:c11
 	COMPAT_OBJS = compat/msvc.o compat/winansi.o \
 		compat/win32/flush.o \
 		compat/win32/path-utils.o \
diff --git a/git-compat-util.h b/git-compat-util.h
index da2986e652fee7..dd055abdfad4c8 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -443,6 +443,16 @@ char *gitdirname(char *);
 # include <sys/sysinfo.h>
 #endif
 
+#ifdef USE_MIMALLOC
+#include "mimalloc.h"
+#define malloc mi_malloc
+#define calloc mi_calloc
+#define realloc mi_realloc
+#define free mi_free
+#define strdup mi_strdup
+#define strndup mi_strndup
+#endif
+
 /* On most systems <netdb.h> would have given us this, but
  * not on some systems (e.g. z/OS).
  */