bug 1506848 - switch Windows debug flags from -Zi to -Z7. r=nalexander

We default to -Zi for Windows debug flags, which is for generating debug info
into a PDB file, but clang-cl doesn't actually implement that so -Zi is
an alias for -Z7 in clang-cl:
http://clang.llvm.org/docs/UsersManual.html#id9

sccache has special handling for -Zi because multiple compiles writing
to the same PDB file is not cacheable, so we've always overridden -Zi with -Z7
in CI when using sccache.

Given that everyone should be using clang-cl nowadays and MSVC will no longer
be supported soon, this patch changes the default and removes some PDB
file name flag setting from rules.mk, as well as the no-longer-necessary
overrides from mozconfig.cache.

Differential Revision: https://phabricator.services.mozilla.com/D18264

--HG--
extra : moz-landing-system : lando

build/moz.configure/toolchain.configure

@@ -1298,7 +1298,7 @@ def check_have_64_bit(have_64_bit, compiler_have_64_bit):
 def default_debug_flags(compiler_info, target):
     # Debug info is ON by default.
     if compiler_info.type in ('msvc', 'clang-cl'):
-        return '-Zi'
+        return '-Z7'
     elif target.kernel == 'WINNT' and compiler_info.type == 'clang':
         return '-g -gcodeview'
     return '-g'

build/mozconfig.cache

@@ -75,13 +75,4 @@ if test -n "$bucket"; then
     export CCACHE="$topsrcdir/sccache2/sccache${suffix}"
     export SCCACHE_VERBOSE_STATS=1
     mk_add_options MOZBUILD_MANAGE_SCCACHE_DAEMON=${topsrcdir}/sccache2/sccache
-    case "$platform" in
-    win*)
-        # For now, sccache doesn't support separate PDBs so force debug info to be
-        # in object files.
-        mk_add_options "export COMPILE_PDB_FLAG="
-        mk_add_options "export HOST_PDB_FLAG="
-        mk_add_options "export MOZ_DEBUG_FLAGS=-Z7"
-        ;;
-    esac
 fi

config/rules.mk

@@ -125,24 +125,11 @@ LINK_PDBFILE ?= $(basename $(@F)).pdb
 
 ifndef GNU_CC
 
-#
-# Unless we're building SIMPLE_PROGRAMS, all C++ files share a PDB file per
-# directory. For parallel builds, this PDB file is shared and locked by
-# MSPDBSRV.EXE, starting with MSVC8 SP1. If you're using MSVC 7.1 or MSVC8
-# without SP1, don't do parallel builds.
-#
-# The final PDB for libraries and programs is created by the linker and uses
-# a different name from the single PDB file created by the compiler. See
-# bug 462740.
-#
-
 ifdef SIMPLE_PROGRAMS
 COMPILE_PDB_FLAG ?= -Fd$(basename $(@F)).pdb
-else
-COMPILE_PDB_FLAG ?= -Fdgenerated.pdb -FS
-endif
 COMPILE_CFLAGS += $(COMPILE_PDB_FLAG)
 COMPILE_CXXFLAGS += $(COMPILE_PDB_FLAG)
+endif
 
 ifdef MOZ_DEBUG
 CODFILE=$(basename $(@F)).cod
@@ -166,8 +153,6 @@ endif
 ifeq ($(HOST_OS_ARCH),WINNT)
 HOST_PDBFILE=$(basename $(@F)).pdb
 HOST_PDB_FLAG ?= -Fd$(HOST_PDBFILE)
-HOST_CFLAGS += $(HOST_PDB_FLAG)
-HOST_CXXFLAGS += $(HOST_PDB_FLAG)
 HOST_C_LDFLAGS += $(HOST_PDB_FLAG)
 HOST_CXX_LDFLAGS += $(HOST_PDB_FLAG)
 endif