CMake: Add support building Qt with the 'mold' linker

The mold linker is a new linker for Linux that provides faster link
times compared to BFD ld, ld.gold and lld.

It can be found at https://github.com/rui314/mold

To build Qt with mold, ensure that the binary in your PATH and then
configure Qt with with either

 cmake /path/to/qtbase -DINPUT_linker=mold

or

 /path/to/qtbase/configure --linker mold

The change was tested with gcc 9, clang 10, clang 12, mold
1.0.0. Only qtbase and qtdeclarative (and dependencies) were tested.

Pick-to: 6.2 6.3
Task-number: QTBUG-99270
Change-Id: I2e64a1f4257c37ff5b64a9326e548b9b46e07c80
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 29 insertions, 1 deletions

diff --git a/configure.cmake b/configure.cmake
index 6cb93ad918..2818db7281 100644
--- a/configure.cmake
+++ b/configure.cmake
@@ -39,6 +39,18 @@ qt_internal_check_if_linker_is_available(use_lld_linker
     FLAG "-fuse-ld=lld"
     )
 
+# We set an invalid flag as a default flag so the compile test fails
+# in case if no mold is found in PATH.
+set(__qt_internal_mold_linker_flags "-Wl,-invalid-flag")
+if(NOT QT_CONFIGURE_RUNNING)
+    qt_internal_get_mold_linker_flags(__qt_internal_mold_linker_flags)
+endif()
+qt_internal_check_if_linker_is_available(use_mold_linker
+    LABEL "mold linker"
+    FLAG "${__qt_internal_mold_linker_flags}"
+    )
+unset(__qt_internal_mold_linker_flags)
+
 qt_feature("use_bfd_linker"
     PRIVATE
     LABEL "bfd"
@@ -46,6 +58,7 @@ qt_feature("use_bfd_linker"
     CONDITION NOT WIN32 AND NOT INTEGRITY AND NOT WASM AND TEST_use_bfd_linker
     ENABLE INPUT_linker STREQUAL 'bfd'
     DISABLE INPUT_linker STREQUAL 'gold' OR INPUT_linker STREQUAL 'lld'
+            OR INPUT_linker STREQUAL 'mold'
 )
 qt_feature_config("use_bfd_linker" QMAKE_PRIVATE_CONFIG)
 
@@ -60,6 +73,7 @@ qt_feature("use_gold_linker"
     CONDITION NOT WIN32 AND NOT INTEGRITY AND NOT WASM AND NOT rtems AND TEST_use_gold_linker
     ENABLE INPUT_linker STREQUAL 'gold' OR QT_FEATURE_use_gold_linker_alias
     DISABLE INPUT_linker STREQUAL 'bfd' OR INPUT_linker STREQUAL 'lld'
+            OR INPUT_linker STREQUAL 'mold'
 )
 qt_feature_config("use_gold_linker" QMAKE_PRIVATE_CONFIG)
 
@@ -70,14 +84,27 @@ qt_feature("use_lld_linker"
     CONDITION NOT WIN32 AND NOT INTEGRITY AND NOT WASM AND TEST_use_lld_linker
     ENABLE INPUT_linker STREQUAL 'lld'
     DISABLE INPUT_linker STREQUAL 'bfd' OR INPUT_linker STREQUAL 'gold'
+            OR INPUT_linker STREQUAL 'mold'
 )
 qt_feature_config("use_lld_linker" QMAKE_PRIVATE_CONFIG)
 
+qt_feature("use_mold_linker"
+    PRIVATE
+    LABEL "mold"
+    AUTODETECT FALSE
+    CONDITION NOT WIN32 AND NOT INTEGRITY AND NOT WASM AND TEST_use_mold_linker
+    ENABLE INPUT_linker STREQUAL 'mold'
+    DISABLE INPUT_linker STREQUAL 'bfd' OR INPUT_linker STREQUAL 'gold'
+            OR INPUT_linker STREQUAL 'lld'
+)
+qt_feature_config("use_mold_linker" QMAKE_PRIVATE_CONFIG)
+
 if(NOT QT_CONFIGURE_RUNNING)
     qt_evaluate_feature(use_bfd_linker)
     qt_evaluate_feature(use_gold_linker_alias)
     qt_evaluate_feature(use_gold_linker)
     qt_evaluate_feature(use_lld_linker)
+    qt_evaluate_feature(use_mold_linker)
 endif()
 
 
@@ -1004,9 +1031,10 @@ qt_configure_add_summary_entry(
 )
 qt_configure_add_summary_entry(
     TYPE "firstAvailableFeature"
-    ARGS "use_bfd_linker use_gold_linker use_lld_linker"
+    ARGS "use_bfd_linker use_gold_linker use_lld_linker use_mold_linker"
     MESSAGE "Linker"
     CONDITION QT_FEATURE_use_bfd_linker OR QT_FEATURE_use_gold_linker OR QT_FEATURE_use_lld_linker
+              OR QT_FEATURE_use_mold_linker
 )
 qt_configure_add_summary_entry(
     ARGS "enable_new_dtags"