sys-devel/llvm: Apply -mno-bmi to work-around gcc-7 bug

Thanks to Alexander Bezrukov for finding the upstream bug and suggesting
a proper workaround.

Closes: https://bugs.gentoo.org/649880

3 files changed, 21 insertions, 9 deletions

diff --git a/sys-devel/llvm/llvm-6.0.0.ebuild b/sys-devel/llvm/llvm-6.0.0.ebuild
index f38524606bb8..cf9585069ad3 100644
--- a/sys-devel/llvm/llvm-6.0.0.ebuild
+++ b/sys-devel/llvm/llvm-6.0.0.ebuild
@@ -75,15 +75,6 @@ S=${WORKDIR}/${P/_/}.src
 # least intrusive of all
 CMAKE_BUILD_TYPE=RelWithDebInfo
 
-pkg_pretend() {
-	if tc-is-gcc && [[ $(gcc-major-version) -ge 7 ]]; then
-		eerror "GCC 7 is known to cause mis-compilation that causes the build to hang."
-		eerror "Please use an older version to build LLVM until a good solution is found."
-		eerror "Bug report: https://bugs.gentoo.org/649880"
-		die "GCC-7+ is not supported"
-	fi
-}
-
 src_prepare() {
 	# Fix llvm-config for shared linking and sane flags
 	# https://bugs.gentoo.org/show_bug.cgi?id=565358
@@ -179,6 +170,13 @@ multilib_src_configure() {
 		)
 	fi
 
+	# workaround BMI bug in gcc-7 (fixed in 7.4)
+	# https://bugs.gentoo.org/649880
+	if tc-is-gcc && [[ $(gcc-major-version) -eq 7 && $(gcc-minor-version) -lt 4 ]]; then
+		local CFLAGS="${CFLAGS} -mno-bmi"
+		local CXXFLAGS="${CXXFLAGS} -mno-bmi"
+	fi
+
 	# LLVM_ENABLE_ASSERTIONS=NO does not guarantee this for us, #614844
 	use debug || local -x CPPFLAGS="${CPPFLAGS} -DNDEBUG"
 	cmake-utils_src_configure
diff --git a/sys-devel/llvm/llvm-6.0.9999.ebuild b/sys-devel/llvm/llvm-6.0.9999.ebuild
index 38353f69eef9..631422bd1ad4 100644
--- a/sys-devel/llvm/llvm-6.0.9999.ebuild
+++ b/sys-devel/llvm/llvm-6.0.9999.ebuild
@@ -170,6 +170,13 @@ multilib_src_configure() {
 		)
 	fi
 
+	# workaround BMI bug in gcc-7 (fixed in 7.4)
+	# https://bugs.gentoo.org/649880
+	if tc-is-gcc && [[ $(gcc-major-version) -eq 7 && $(gcc-minor-version) -lt 4 ]]; then
+		local CFLAGS="${CFLAGS} -mno-bmi"
+		local CXXFLAGS="${CXXFLAGS} -mno-bmi"
+	fi
+
 	# LLVM_ENABLE_ASSERTIONS=NO does not guarantee this for us, #614844
 	use debug || local -x CPPFLAGS="${CPPFLAGS} -DNDEBUG"
 	cmake-utils_src_configure
diff --git a/sys-devel/llvm/llvm-9999.ebuild b/sys-devel/llvm/llvm-9999.ebuild
index 603571a0bd65..1c439e6fd6a5 100644
--- a/sys-devel/llvm/llvm-9999.ebuild
+++ b/sys-devel/llvm/llvm-9999.ebuild
@@ -172,6 +172,13 @@ multilib_src_configure() {
 		)
 	fi
 
+	# workaround BMI bug in gcc-7 (fixed in 7.4)
+	# https://bugs.gentoo.org/649880
+	if tc-is-gcc && [[ $(gcc-major-version) -eq 7 && $(gcc-minor-version) -lt 4 ]]; then
+		local CFLAGS="${CFLAGS} -mno-bmi"
+		local CXXFLAGS="${CXXFLAGS} -mno-bmi"
+	fi
+
 	# LLVM_ENABLE_ASSERTIONS=NO does not guarantee this for us, #614844
 	use debug || local -x CPPFLAGS="${CPPFLAGS} -DNDEBUG"
 	cmake-utils_src_configure