feat(C++ modules) add build.c++.modules.non_cascading_changes policy to enable bmi hash comparison as incremental build optimisation for clang

3 files changed, 43 insertions, 10 deletions

diff --git a/xmake/core/project/policy.lua b/xmake/core/project/policy.lua
index 6949a6b94..967f9062e 100644
--- a/xmake/core/project/policy.lua
+++ b/xmake/core/project/policy.lua
@@ -72,6 +72,8 @@ function policy.policies()
             ["build.rpath"]                       = {description = "Enable build rpath.", default = true, type = "boolean"},
             -- Enable C++ modules for C++ building, even if no .mpp is involved in the compilation
             ["build.c++.modules"]                 = {description = "Enable C++ modules for C++ building.", type = "boolean"},
+            -- Enable non cascading changes (experimental)
+            ["build.c++.modules.non_cascading_changes"] = {description = "Enable non cascading changes when supported (experimental).", default = false, type = "boolean"},
             -- Hide C++ required files to reduce noise (may reduce build performance)
             ["build.c++.modules.hide_dependencies"] = {description = "Hide dependencies from the commandline when build C++ modules.", default = false, type = "boolean"},
             -- Enable two phase compilation for C++ modules if supported by the compiler
diff --git a/xmake/rules/c++/modules/builder.lua b/xmake/rules/c++/modules/builder.lua
index b84d5d23e..a1c93a35f 100644
--- a/xmake/rules/c++/modules/builder.lua
+++ b/xmake/rules/c++/modules/builder.lua
@@ -180,6 +180,15 @@ function should_build(target, module)
         local old_dependinfo = target:is_rebuilt() and {} or (depend.load(dependfile) or {})
         old_dependinfo.files = {module.sourcefile}
 
+        -- need build this object?
+        local dryrun = option.get("dry-run")
+        if dryrun or depend.is_changed(old_dependinfo, dependinfo) then
+            depend.save(dependinfo, dependfile)
+            memcache:set2(target:fullname(), "should_build_" .. module.sourcefile, true)
+            profiler.leave(target:fullname(), "c++ modules", "builder", "check if " .. (module.name or module.sourcefile) .. " should be rebuilt")
+            return true
+        end
+
         -- force rebuild a module if any of its module dependency is rebuilt
         for dep_name, dep_module in table.orderpairs(module.deps) do
             local mapped_dep = mapper.get(target, dep_module.headerunit and dep_name .. dep_module.key or dep_name)
@@ -188,18 +197,10 @@ function should_build(target, module)
                 depend.save(dependinfo, dependfile)
                 memcache:set2(target:fullname(), "should_build_" .. module.sourcefile, true)
                 profiler.leave(target:fullname(), "c++ modules", "builder", "check if " .. (module.name or module.sourcefile) .. " should be rebuilt")
-                return true
+                return true, true
             end
         end
 
-        -- need build this object?
-        local dryrun = option.get("dry-run")
-        if dryrun or depend.is_changed(old_dependinfo, dependinfo) then
-            depend.save(dependinfo, dependfile)
-            memcache:set2(target:fullname(), "should_build_" .. module.sourcefile, true)
-            profiler.leave(target:fullname(), "c++ modules", "builder", "check if " .. (module.name or module.sourcefile) .. " should be rebuilt")
-            return true
-        end
         memcache:set2(target:fullname(), "should_build_" .. module.sourcefile, false)
         profiler.leave(target:fullname(), "c++ modules", "builder", "check if " .. (module.name or module.sourcefile) .. " should be rebuilt")
         return false
diff --git a/xmake/rules/c++/modules/clang/builder.lua b/xmake/rules/c++/modules/clang/builder.lua
index 684a6a030..60f2186e5 100644
--- a/xmake/rules/c++/modules/clang/builder.lua
+++ b/xmake/rules/c++/modules/clang/builder.lua
@@ -20,6 +20,7 @@
 
 -- imports
 import("core.base.json")
+import("core.base.bytes")
 import("core.base.option")
 import("core.base.semver")
 import("utils.progress")
@@ -46,6 +47,19 @@ function _get_bmifile(target, module)
     return bmifile, add_reduced_flag
 end
 
+function _update_bmihash(target, module)
+    local localcache = support.localcache()
+
+    local bmifile = _get_bmifile(target, module)
+    local bmihash = hash.xxhash128(bytes(io.readfile(bmifile)))
+    local old_bmihash = localcache:get2(bmifile, "hash")
+
+    if not old_bmihash or bmihash ~= old_bmihash then
+        localcache:set2(bmifile, "hash", bmihash)
+        support.memcache():set2(bmifile, "updated", true)
+    end
+end
+
 function _make_modulebuildflags(target, module, opt)
     assert(not module.headerunit)
 
@@ -285,11 +299,23 @@ end
 function make_module_job(target, module, opt)
 
     local dryrun = option.get("dry-run")
+    local enable_hash_comparison = target:policy("build.c++.modules.non_cascading_changes")
 
-    local build = should_build(target, module)
+    local build, because_of_dependencies = should_build(target, module)
     local bmi = opt and opt.bmi
     local objectfile = opt and opt.objectfile
 
+    if build and enable_hash_comparison and because_of_dependencies then
+        build = false
+        for dep_name, dep_module in table.orderpairs(module.deps) do
+            local mapped_dep = mapper.get(target, dep_module.headerunit and dep_name .. dep_module.key or dep_name)
+            if support.memcache():get2(_get_bmifile(target, dep_module), "updated") then
+                build = true
+                break
+            end
+        end
+    end
+
     if build then
         if not dryrun then
             local objectdir = path.directory(module.objectfile)
@@ -315,6 +341,10 @@ function make_module_job(target, module, opt)
                 os.tryrm(module.objectfile) -- force rebuild for .cpp files
             end
         end
+
+        if enable_hash_comparison and bmi then
+            _update_bmihash(target, module)
+        end
     end
 end