This also causes QtWebEngine to FTBFS for ARM:

FAILED: /usr/bin/gcc -MMD -MF obj/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/common_audio_neon.downsample_fast_neon.o.d -DV8_DEPRECATION_WARNINGS -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -DNO_TCMALLOC -DCHROMIUM_BUILD -DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_DEFAULT_RENDER_THEME=1 -DUSE_LIBJPEG_TURBO=1 -DUSE_X11=1 -DENABLE_ONE_CLICK_SIGNIN -DENABLE_PRE_SYNC_BACKUP -DENABLE_REMOTING=1 -DENABLE_WEBRTC=1 -DENABLE_MEDIA_ROUTER=1 -DENABLE_PEPPER_CDMS -DENABLE_CONFIGURATION_POLICY -DENABLE_NOTIFICATIONS -DENABLE_HIDPI=1 -DENABLE_TOPCHROME_MD=1 -DUSE_UDEV -DDONT_EMBED_BUILD_METADATA -DENABLE_TASK_MANAGER=1 -DENABLE_EXTENSIONS=1 -DENABLE_PLUGINS=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_THEMES=1 -DENABLE_AUTOFILL_DIALOG=1 -DENABLE_BACKGROUND=1 -DENABLE_GOOGLE_NOW=1 -DCLD_VERSION=2 -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_APP_LIST=1 -DENABLE_SETTINGS_APP=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_
MDNS=1 -DENABLE_SERVICE_DISCOVERY=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DSAFE_BROWSING_SERVICE -DWEBRTC_RESTRICT_LOGGING -DEXPAT_RELATIVE_PATH -DWEBRTC_CHROMIUM_BUILD -DLOGGING_INSIDE_WEBRTC -DWEBRTC_ARCH_ARM -DWEBRTC_ARCH_ARM_V7 -DWEBRTC_HAS_NEON -DWEBRTC_POSIX -DWEBRTC_LINUX -DUSE_LIBPCI=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -D_FORTIFY_SOURCE=2 -Igen -I/builddir/build/BUILD/qtwebengine-opensource-src-5.6.0-beta/src/3rdparty/chromium -I/builddir/build/BUILD/qtwebengine-opensource-src-5.6.0-beta/src/3rdparty/chromium/third_party/webrtc/overrides -I/builddir/build/BUILD/qtwebengine-opensource-src-5.6.0-beta/src/3rdparty/chromium/third_party -I/usr/include/libdrm -fstack-protector --param=ssp-buffer-size=4  -pthread -fno-strict-aliasing -Wall -Wno-unused-parameter -Wno-missing-field-initializers -fvisibility=hidden -pipe -fPIC -Wno-unused-local-typedefs -mfpu=neon -I/usr/include/dbus-1.
0 -I/usr/lib/dbus-1.0/include -march=armv7-a -mtune=generic-armv7-a -mfpu=neon -mfloat-abi=hard -mthumb -O2 -fno-ident -fdata-sections -ffunction-sections -funwind-tables   -c /builddir/build/BUILD/qtwebengine-opensource-src-5.6.0-beta/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/downsample_fast_neon.c -o obj/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/common_audio_neon.downsample_fast_neon.o
*** stack smashing detected ***: /usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1 terminated
======= Backtrace: =========
/lib/libc.so.6(+0x6a538)[0xb6c8b538]
/lib/libc.so.6(__fortify_fail+0x40)[0xb6d19a6c]
/lib/libc.so.6(__stack_chk_fail+0x10)[0xb6d19a28]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z18arm_expand_builtinP9tree_nodeP7rtx_defS2_12machine_modei+0x19ec)[0x2ff6b4]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z14expand_builtinP9tree_nodeP7rtx_defS2_12machine_modei+0x1d64)[0x4c0150]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z18expand_expr_real_1P9tree_nodeP7rtx_def12machine_mode15expand_modifierPS2_b+0x211c)[0x5a2978]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z22store_expr_with_boundsP9tree_nodeP7rtx_defibS0_+0xd8)[0x5a6b10]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z17expand_assignmentP9tree_nodeS0_b+0x17c)[0x5a4f50]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1[0x4d9d90]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1[0x4d1400]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z16execute_one_passP8opt_pass+0x154)[0x711714]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z17execute_pass_listP8functionP8opt_pass+0x24)[0x714460]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_ZN12symbol_table7compileEv+0x56c)[0xb80350]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_ZN12symbol_table25finalize_compilation_unitEv+0x70)[0xb7fb1c]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_Z27c_write_global_declarationsv+0x11c)[0x4323d8]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1[0xbec814]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(_ZN6toplev4mainEiPPc+0xb5c)[0x422b58]
/usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1(main+0x40)[0x4235e0]
/lib/libc.so.6(__libc_start_main+0x114)[0xb6c37df8]
======= Memory map: ========
00010000-01052000 r-xp 00000000 08:03 3279223    /usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1
01061000-0106f000 rw-p 01041000 08:03 3279223    /usr/libexec/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/cc1
0106f000-0112f000 rw-p 00000000 00:00 0 
02d87000-02e52000 rw-p 00000000 00:00 0          [heap]
b6372000-b6776000 rw-p 00000000 00:00 0 
b67e0000-b6bf4000 rw-p 00000000 00:00 0 
b6bf4000-b6c11000 r-xp 00000000 08:03 2884013    /usr/lib/libgcc_s-5.3.1-20151207.so.1
b6c11000-b6c20000 ---p 0001d000 08:03 2884013    /usr/lib/libgcc_s-5.3.1-20151207.so.1
b6c20000-b6c21000 rw-p 0001c000 08:03 2884013    /usr/lib/libgcc_s-5.3.1-20151207.so.1
b6c21000-b6d69000 r-xp 00000000 08:03 2884879    /usr/lib/libc-2.22.90.so
b6d69000-b6d79000 ---p 00148000 08:03 2884879    /usr/lib/libc-2.22.90.so
b6d79000-b6d7b000 r--p 00148000 08:03 2884879    /usr/lib/libc-2.22.90.so
b6d7b000-b6d7c000 rw-p 0014a000 08:03 2884879    /usr/lib/libc-2.22.90.so
b6d7c000-b6d7f000 rw-p 00000000 00:00 0 
b6d7f000-b6df0000 r-xp 00000000 08:03 2884887    /usr/lib/libm-2.22.90.so
b6df0000-b6e00000 ---p 00071000 08:03 2884887    /usr/lib/libm-2.22.90.so
b6e00000-b6e01000 r--p 00071000 08:03 2884887    /usr/lib/libm-2.22.90.so
b6e01000-b6e02000 rw-p 00072000 08:03 2884887    /usr/lib/libm-2.22.90.so
b6e02000-b6e14000 r-xp 00000000 08:03 2885052    /usr/lib/libz.so.1.2.8
b6e14000-b6e24000 ---p 00012000 08:03 2885052    /usr/lib/libz.so.1.2.8
b6e24000-b6e25000 r--p 00012000 08:03 2885052    /usr/lib/libz.so.1.2.8
b6e25000-b6e26000 rw-p 00013000 08:03 2885052    /usr/lib/libz.so.1.2.8
b6e26000-b6e85000 r-xp 00000000 08:03 2885067    /usr/lib/libgmp.so.10.3.0
b6e85000-b6e95000 ---p 0005f000 08:03 2885067    /usr/lib/libgmp.so.10.3.0
b6e95000-b6e96000 rw-p 0005f000 08:03 2885067    /usr/lib/libgmp.so.10.3.0
b6e96000-b6eeb000 r-xp 00000000 08:03 2885151    /usr/lib/libmpfr.so.4.1.3
b6eeb000-b6efa000 ---p 00055000 08:03 2885151    /usr/lib/libmpfr.so.4.1.3
b6efa000-b6efb000 r--p 00054000 08:03 2885151    /usr/lib/libmpfr.so.4.1.3
b6efb000-b6efc000 rw-p 00000000 00:00 0 
b6efc000-b6f0e000 r-xp 00000000 08:03 2885159    /usr/lib/libmpc.so.3.0.0
b6f0e000-b6f1e000 ---p 00012000 08:03 2885159    /usr/lib/libmpc.so.3.0.0
b6f1e000-b6f1f000 r--p 00012000 08:03 2885159    /usr/lib/libmpc.so.3.0.0
b6f1f000-b6f20000 rw-p 00000000 00:00 0 
b6f20000-b6f24000 r-xp 00000000 08:03 2884885    /usr/lib/libdl-2.22.90.so
b6f24000-b6f33000 ---p 00004000 08:03 2884885    /usr/lib/libdl-2.22.90.so
b6f33000-b6f34000 r--p 00003000 08:03 2884885    /usr/lib/libdl-2.22.90.so
b6f34000-b6f35000 rw-p 00004000 08:03 2884885    /usr/lib/libdl-2.22.90.so
b6f35000-b6f58000 r-xp 00000000 08:03 2884871    /usr/lib/ld-2.22.90.so
b6f59000-b6f5f000 rw-p 00000000 00:00 0 
b6f5f000-b6f67000 rw-p 00000000 00:00 0 
b6f67000-b6f68000 r--p 00022000 08:03 2884871    /usr/lib/ld-2.22.90.so
b6f68000-b6f69000 rw-p 00023000 08:03 2884871    /usr/lib/ld-2.22.90.so
be97b000-be99d000 rw-p 00000000 00:00 0          [stack]
be9d8000-be9d9000 r-xp 00000000 00:00 0          [sigpage]
ffff0000-ffff1000 r-xp 00000000 00:00 0          [vectors]
In file included from /builddir/build/BUILD/qtwebengine-opensource-src-5.6.0-beta/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/downsample_fast_neon.c:13:0:
/usr/lib/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/include/arm_neon.h: In function 'WebRtcSpl_DownsampleFastNeon':
/usr/lib/gcc/armv7hl-redhat-linux-gnueabi/5.3.1/include/arm_neon.h:6697:10: internal compiler error: Aborted
   return (int32x4_t)__builtin_neon_vmlals_lanev4hi (__a, __b, __c, __d);
          ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://bugzilla.redhat.com/bugzilla> for instructions.
The bug is not reproducible, so it is likely a hardware or OS problem.
ninja: build stopped: subcommand failed.
Makefile.gyp_run:290: recipe for target 'invoke_ninja' failed

Other Chromium forks are affected too: Ubuntu was hitting this with their ozone-qt:
https://bugs.launchpad.net/ubuntu/+source/oxide-qt/+bug/1527741
and they found this to be a regression from the fix to PR63870:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63870

GCC claims the bug is not reproducible, but I tried resubmitting the build twice, and all my 3 build attempts failed at the same place with the same error.

(I've set the priority to urgent because this breaks the build of a key component of Qt 5.6.)

I'm building QtWebEngine with NEON completely disabled now, which kinda sucks, but at least it avoids running into this ICE.

This is upstream https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69187 - I have attached a proprosed fix there.

Can we please get this fixed? As far as I can tell, this affects GCC on all currently supported Fedora releases, the fix is trivial, and getting this fixed would allow me to build QtWebEngine with arm_neon_optional enabled rather than disabling NEON entirely.

Ping? As far as I can tell, this is now fixed in F24 and Rawhide by updating GCC, but F22 and F23 are still affected. There is a 5.3.1-4 that claims to fix this in F23 dist-git, but it is not pushed anywhere, nor was it merged to the F22 branch.

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F23 updates has gcc-5.3.1-6.fc23 now.