https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80264
Bug ID: 80264 Summary: g++ ignores register assignments in template functions Product: gcc Version: 7.0.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: blubban at gmail dot com Target Milestone: --- Created attachment 41092 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41092&action=edit Testcase Input (also attached): template<int x> void foo1() { register int bar asm("NOT-A-REGISTER"); } template void foo1<0>(); template<int x> void foo2() { register int edi asm("edi") = 42; asm volatile("" :: "r"(edi)); } template void foo2<0>(); void foo3() { register int edi asm("edi") = 42; asm volatile("" :: "r"(edi)); } Command line: g++ -S template-inline-asm.cpp -o- (the flags don't affect this issue) Expected output: First function: error: invalid register name for 'bar' Second: movl $42, %edi (or equivalent) Third: movl $42, %edi Actual output: First one: Compiler silently emits a blank function (other than an unused variable warning) Second: movl $42, %ebx (%eax on -O1 or higher) Third: As expected Tested versions: g++ 7.0.1 20170330 x86_64-linux-gnu (Godbolt) g++ 6.2.0-5ubuntu12 x86_64-linux-gnu (Lubuntu 16.10) g++ 4.4.7-1ubuntu2 x86_64-linux-gnu (Godbolt) clang++ 3.8.1-12ubuntu1 (acts as expected) 7.0.1 config: Using built-in specs. COLLECT_GCC=/opt/compiler-explorer/gcc-7-snapshot/bin/g++ Target: x86_64-linux-gnu Configured with: ../gcc-trunk-20170330/configure --prefix /root/staging --build=x86_64-linux-gnu --disable-multilibs --disable-bootstrap --enable-clocale=gnu --enable-languages=c,c++ --enable-ld=yes --enable-gold=yes --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-linker-build-id --enable-lto --enable-plugins --enable-threads=posix --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-pkgversion=GCC-Explorer-Build Thread model: posix gcc version 7.0.1 20170330 (experimental) (GCC-Explorer-Build) COLLECT_GCC_OPTIONS='-g' '-o' '/tmp/compiler-explorer-compiler117230-57-19womo8.vtf1hmpldi/output.s' '-masm=intel' '-S' '-v' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /opt/compiler-explorer/gcc-trunk-20170330/bin/../libexec/gcc/x86_64-linux-gnu/7.0.1/cc1plus -quiet -v -imultiarch x86_64-linux-gnu -iprefix /opt/compiler-explorer/gcc-trunk-20170330/bin/../lib/gcc/x86_64-linux-gnu/7.0.1/ -D_GNU_SOURCE <source> -quiet -dumpbase example.cpp -masm=intel -mtune=generic -march=x86-64 -auxbase-strip /tmp/compiler-explorer-compiler117230-57-19womo8.vtf1hmpldi/output.s -g -version -o /tmp/compiler-explorer-compiler117230-57-19womo8.vtf1hmpldi/output.s GNU C++14 (GCC-Explorer-Build) version 7.0.1 20170330 (experimental) (x86_64-linux-gnu) compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3, isl version isl-0.16.1-GMP GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096