Bump __GNUC__, __GNUC_MINOR__ from 4.2.1

[davidbolvansky]

Bugzilla Link	42817
Version	trunk
OS	Linux
CC	@zygoloid,@sylvestre

Extended Description

ICC:

printf("%d %d %d %d %s",__GXX_ABI_VERSION, GNUC, GNUC_MINOR, GNUC_PATCHLEVEL, VERSION);

1010 7 4 0 Intel(R) C++ gcc 7.4 mode

Clang's current gcc-compat version "4.2.1" is very old and may force Clang to take path for dump, old compilers.

[davidbolvansky]

assigned to @sylvestre

[sylvestre]

Which version would you like to see? Same as ICC ?

[davidbolvansky]

Yes, 7 could be good enough for now.

[h-vetinari]

We're about to branch LLVM 19, and clang still sets __GNUC__ to 4.2.1

llvm-project/clang/lib/Driver/ToolChains/Clang.cpp

Lines 7041 to 7042 in 0caf0c9

	// Imitate GCC 4.2.1 by default if -fms-compatibility is not in effect.
	GNUCVer = VersionTuple(4, 2, 1);

llvm-project/clang/lib/Frontend/CompilerInvocation.cpp

Lines 3982 to 3991 in 0caf0c9

	VersionTuple GNUCVer;
	bool Invalid = GNUCVer.tryParse(A->getValue());
	unsigned Major = GNUCVer.getMajor();
	unsigned Minor = GNUCVer.getMinor().value_or(0);
	unsigned Patch = GNUCVer.getSubminor().value_or(0);
	if (Invalid || GNUCVer.getBuild() || Minor >= 100 || Patch >= 100) {
	Diags.Report(diag::err_drv_invalid_value)
	<< A->getAsString(Args) << A->getValue();
	}
	Opts.GNUCVersion = Major * 100 * 100 + Minor * 100 + Patch;

llvm-project/clang/lib/Frontend/InitPreprocessor.cpp

Lines 869 to 877 in 0caf0c9

	if (LangOpts.GNUCVersion != 0) {
	// Major, minor, patch, are given two decimal places each, so 4.2.1 becomes
	// 40201.
	unsigned GNUCMajor = LangOpts.GNUCVersion / 100 / 100;
	unsigned GNUCMinor = LangOpts.GNUCVersion / 100 % 100;
	unsigned GNUCPatch = LangOpts.GNUCVersion % 100;
	Builder.defineMacro("__GNUC__", Twine(GNUCMajor));
	Builder.defineMacro("__GNUC_MINOR__", Twine(GNUCMinor));
	Builder.defineMacro("__GNUC_PATCHLEVEL__", Twine(GNUCPatch));

[zygoloid]

We should do this, but any bump in version here will need some careful testing. Historically there were standard C libraries (eg glibc) that used GCC features that Clang didn't support if the reported GCC version was set above some relatively low number (I think it was around 4.7, but that's a very vague memory). It could be that Clang implements enough GCC extensions these days that we can bump the version number a fair bit, but it's not straightforward to work out by how much.