Add llvm linker detection to configure

https://gcc.gnu.org/ml/gcc-patches/2018-10/msg01240.html

This is currently only used for webengine, where link time really matters.

New configure options:
* force 'lld'  '-linker lld' or' --linker=lld'
* force 'gold' '-linker gold' or '--linker=gold'
* force 'bfd' '-linker bfd' or '--linker=bfd'

Note before by default gold was always forced (if supported) now default linker
is system default one.

[ChangeLog][Tools][configure & build system] Added --linker=[bfg,lld,gold] configure flag.

Change-Id: Idaa13510da70243c6176b96db846d629cd65c7af
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

6 files changed, 74 insertions, 6 deletions

diff --git a/config_help.txt b/config_help.txt
index 223adf61d7..8eea64e03a 100644
--- a/config_help.txt
+++ b/config_help.txt
@@ -167,7 +167,8 @@ Build options:
 
   -pch ................. Use precompiled headers [auto]
   -ltcg ................ Use Link Time Code Generation [no]
-  -use-gold-linker ..... Use the GNU gold linker [auto]
+  -linker [bfd,gold,lld] Force use of the GNU ld, GNU gold or LLVM/LLD linker
+                         instead of default one (GCC only)
   -incredibuild-xge .... Use the IncrediBuild XGE [no] (Windows only)
   -ccache .............. Use the ccache compiler cache [no] (Unix only)
   -make-tool <tool> .... Use <tool> to build qmake [nmake] (Windows only)
diff --git a/configure.json b/configure.json
index f1a414fbf9..4a9e1fc24e 100644
--- a/configure.json
+++ b/configure.json
@@ -90,6 +90,7 @@
             "headersclean": "boolean",
             "incredibuild-xge": { "type": "boolean", "name": "incredibuild_xge" },
             "libudev": "boolean",
+            "linker": { "type": "optionalString", "values": [ "bfd", "gold", "lld" ] },
             "ltcg": "boolean",
             "make": { "type": "addString", "values": [ "examples", "libs", "tests", "tools" ] },
             "make-tool": "string",
@@ -131,7 +132,7 @@
             "syncqt": "boolean",
             "sysroot": "string",
             "testcocoon": "boolean",
-            "use-gold-linker": { "type": "boolean", "name": "use_gold_linker" },
+            "use-gold-linker": { "type": "boolean", "name": "use_gold_linker_alias" },
             "warnings-are-errors": { "type": "boolean", "name": "warnings_are_errors" },
             "Werror": { "type": "boolean", "name": "warnings_are_errors" },
             "widgets": "boolean",
@@ -224,8 +225,8 @@
     },
 
     "testTypeDependencies": {
-        "linkerSupportsFlag": [ "use_gold_linker" ],
-        "verifySpec": [ "shared", "use_gold_linker", "compiler-flags", "qmakeargs", "commit" ],
+        "linkerSupportsFlag": [ "use_bfd_linker", "use_gold_linker", "use_lld_linker" ],
+        "verifySpec": [ "shared", "use_bfd_linker", "use_gold_linker", "use_lld_linker", "compiler-flags", "qmakeargs", "commit" ],
         "compile": [ "verifyspec" ],
         "detectPkgConfig": [ "cross_compile", "machineTuple" ],
         "library": [ "pkg-config", "compiler-flags" ],
@@ -357,11 +358,21 @@
                 ]
             }
         },
+        "use_bfd_linker": {
+            "label": "bfd linker",
+            "type": "compilerSupportsFlag",
+            "flag": "-fuse-ld=bfd"
+        },
         "use_gold_linker": {
             "label": "gold linker",
             "type": "compilerSupportsFlag",
             "flag": "-fuse-ld=gold"
         },
+        "use_lld_linker" : {
+            "label": "lld linker",
+            "type": "compilerSupportsFlag",
+            "flag": "-fuse-ld=lld"
+        },
         "optimize_debug": {
             "label": "-Og support",
             "type": "compilerSupportsFlag",
@@ -649,11 +660,34 @@
             "output": [ "qmakeArgs" ],
             "condition": "input.qmakeArgs != ''"
         },
+        "use_bfd_linker": {
+            "label": "bfd",
+            "autoDetect": "false",
+            "enable" : "input.linker == 'bfd'",
+            "disable" : "input.linker == 'gold' || input.linker == 'lld'",
+            "condition": "!config.win32 && !config.integrity && !config.wasm && tests.use_bfd_linker",
+            "output": [ "privateConfig", "useBFDLinker" ]
+        },
+        "use_gold_linker_alias": {
+            "autoDetect": "false",
+            "condition": "!config.win32 && !config.integrity && !config.wasm && tests.use_gold_linker"
+        },
         "use_gold_linker": {
-            "label": "Using gold linker",
+            "label": "gold",
+            "autoDetect": "false",
+            "enable" : "input.linker == 'gold' || features.use_gold_linker_alias" ,
+            "disable" : "input.linker == 'bfd' || input.linker == 'lld'",
             "condition": "!config.win32 && !config.integrity && !config.wasm && tests.use_gold_linker",
             "output": [ "privateConfig", "useGoldLinker" ]
         },
+        "use_lld_linker": {
+            "label": "lld",
+            "autoDetect": "false",
+            "enable" : "input.linker == 'lld'",
+            "disable" : "input.linker == 'bfd' || input.linker == 'gold'",
+            "condition": "!config.win32 && !config.integrity && !config.wasm && tests.use_lld_linker",
+            "output": [ "privateConfig", "useLLDLinker" ]
+        },
         "optimize_debug": {
             "label": "Optimize debug build",
             "condition": "!config.msvc && !config.clang && (features.debug || features.debug_and_release) && tests.optimize_debug",
@@ -1386,7 +1420,12 @@ Configure with '-qreal float' to create a build that is binary-compatible with 5
                     "args": "ccache",
                     "condition": "config.unix"
                 },
-                "use_gold_linker",
+                {
+                    "message": "Linker",
+                    "type": "firstAvailableFeature",
+                    "args": "use_bfd_linker use_gold_linker use_lld_linker",
+                    "condition": "features.use_bfd_linker || features.use_gold_linker || features.use_lld_linker"
+                },
                 {
                     "type": "feature",
                     "args": "enable_new_dtags",
diff --git a/configure.pri b/configure.pri
index df890a7c49..d92653885f 100644
--- a/configure.pri
+++ b/configure.pri
@@ -1026,6 +1026,14 @@ defineTest(qtConfOutput_crossCompile) {
     export(CONFIG)
 }
 
+defineTest(qtConfOutput_useBFDLinker) {
+    !$${2}: return()
+
+    # We need to preempt the output here, so that qtConfTest_linkerSupportsFlag can work properly in qtbase
+    CONFIG += use_bfd_linker
+    export(CONFIG)
+}
+
 defineTest(qtConfOutput_useGoldLinker) {
     !$${2}: return()
 
@@ -1034,6 +1042,14 @@ defineTest(qtConfOutput_useGoldLinker) {
     export(CONFIG)
 }
 
+defineTest(qtConfOutput_useLLDLinker) {
+    !$${2}: return()
+
+    # We need to preempt the output here, so that qtConfTest_linkerSupportsFlag can work properly in qtbase
+    CONFIG += use_lld_linker
+    export(CONFIG)
+}
+
 defineTest(qtConfOutput_debugAndRelease) {
     $$qtConfEvaluate("features.debug") {
         qtConfOutputVar(append, "publicPro", "CONFIG", "debug")
diff --git a/mkspecs/common/gcc-base-unix.conf b/mkspecs/common/gcc-base-unix.conf
index 700f228c36..a456c8f3eb 100644
--- a/mkspecs/common/gcc-base-unix.conf
+++ b/mkspecs/common/gcc-base-unix.conf
@@ -20,7 +20,9 @@ QMAKE_LFLAGS_RPATH      = -Wl,-rpath,
 QMAKE_LFLAGS_RPATHLINK  = -Wl,-rpath-link,
 QMAKE_LFLAGS_NEW_DTAGS  = -Wl,--enable-new-dtags
 QMAKE_LFLAGS_GDB_INDEX  = -Wl,--gdb-index
+QMAKE_LFLAGS_USE_BFD    = -fuse-ld=bfd
 QMAKE_LFLAGS_USE_GOLD   = -fuse-ld=gold
+QMAKE_LFLAGS_USE_LLD    = -fuse-ld=lld
 
 # -Bsymbolic-functions (ld) support
 QMAKE_LFLAGS_BSYMBOLIC_FUNC = -Wl,-Bsymbolic-functions
diff --git a/mkspecs/features/default_post.prf b/mkspecs/features/default_post.prf
index d90da49781..69da78c5b7 100644
--- a/mkspecs/features/default_post.prf
+++ b/mkspecs/features/default_post.prf
@@ -78,7 +78,9 @@ stack_protector_strong {
 
 # disable special linker flags for host builds (no proper test for host support yet)
 !host_build|!cross_compile {
+    use_bfd_linker: QMAKE_LFLAGS += $$QMAKE_LFLAGS_USE_BFD
     use_gold_linker: QMAKE_LFLAGS += $$QMAKE_LFLAGS_USE_GOLD
+    use_lld_linker: QMAKE_LFLAGS += $$QMAKE_LFLAGS_USE_LLD
     enable_new_dtags: QMAKE_LFLAGS += $$QMAKE_LFLAGS_NEW_DTAGS
     enable_gdb_index: QMAKE_LFLAGS += $$QMAKE_LFLAGS_GDB_INDEX
 }
diff --git a/mkspecs/features/qt_configure.prf b/mkspecs/features/qt_configure.prf
index c45439c3ef..f682892abe 100644
--- a/mkspecs/features/qt_configure.prf
+++ b/mkspecs/features/qt_configure.prf
@@ -368,8 +368,12 @@ defineTest(qtConfTest_compilerSupportsFlag) {
 defineTest(qtConfTest_linkerSupportsFlag) {
     flag = $$eval($${1}.flag)
 
+    use_bfd_linker: \
+        LFLAGS = -fuse-ld=bfd
     use_gold_linker: \
         LFLAGS = -fuse-ld=gold
+    use_lld_linker: \
+        LFLAGS = -fuse-ld=lld
 
     return($$qtConfToolchainSupportsFlag($$LFLAGS "-Wl,$$flag"))
 }
@@ -1220,8 +1224,12 @@ defineTest(qtConfTest_compile) {
     else: \
         qmake_configs = "static"
 
+    use_bfd_linker: \
+        qmake_configs += "use_bfd_linker"
     use_gold_linker: \
         qmake_configs += "use_gold_linker"
+    use_lld_linker: \
+        qmake_configs += "use_lld_linker"
 
     # disable warnings from the builds, since they're just noise at this point.
     qmake_configs += "warn_off"