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ffbuild/common: Fix CPPFLAGS applied for compiling C++ files 

Currently, $(CPPFLAGS) and $(CFLAGS) are prepended to CXXFLAGS
(the flags for compiling C++) like this:
CXXFLAGS := $(CPPFLAGS) $(CFLAGS) $(CXXFLAGS)
Using ":=" creates a simply expanded variable, i.e. the values
of the variable at the time of assignment are used and later
modifications to them are ignored (using a recursively expanding
variable (i.e. "=" instead of ":=") is not really possible here,
as there would be an infinite loop when evaluating CXXFLAGS).

Yet we perform later additions to CPPFLAGS: HAVE_AV_CONFIG_H and
BUILDING_libfoo are defined. These do not reach C++ compilations.

To fix this a trick is employed to prepend to a recursively
expanded variable while keeping it recursively expanded.

There are two practical consequences of this: C++ files now no longer
include the version.h header, but only the version_major.h header
of their library, saving some recompilations. Furthermore, they
now get some optimized math functions (namely the ones from
lavu/intmath.h instead of the ones from lavu/common.h).
(av_parity() is the only one for which it makes a difference.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-05-13 00:16:30 +02:00
parent b033913d1c
commit a78173374a
1 changed files with 6 additions and 1 deletions
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7
ffbuild/common.mak
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@ -29,6 +29,9 @@ $(foreach VAR,$(SILENT),$(eval override $(VAR) = @$($(VAR))))
$(eval INSTALL = @$(call ECHO,INSTALL,$$(^:$(SRC_DIR)/%=%)); $(INSTALL))
endif
# Prepend to a recursively expanded variable without making it simply expanded.
PREPEND = $(eval $(1) = $(patsubst %,$$(%), $(2)) $(value $(1)))
# NASM requires -I path terminated with /
IFLAGS := -I. -I$(SRC_LINK)/
CPPFLAGS := $(IFLAGS) $(CPPFLAGS)
@ -37,7 +40,9 @@ CCFLAGS = $(CPPFLAGS) $(CFLAGS)
OBJCFLAGS += $(EOBJCFLAGS)
OBJCCFLAGS = $(CPPFLAGS) $(CFLAGS) $(OBJCFLAGS)
ASFLAGS := $(CPPFLAGS) $(ASFLAGS)
CXXFLAGS := $(CPPFLAGS) $(CFLAGS) $(CXXFLAGS)
# Use PREPEND here so that later (target-dependent) additions to CPPFLAGS
# end up in CXXFLAGS.
$(call PREPEND,CXXFLAGS, CPPFLAGS CFLAGS)
X86ASMFLAGS += $(IFLAGS:%=%/) -I$(<D)/ -Pconfig.asm
HOSTCCFLAGS = $(IFLAGS) $(HOSTCPPFLAGS) $(HOSTCFLAGS)