[gcc r17-2491] testsuite: Add { dg-lto-do incr-link } option

https://gcc.gnu.org/g:230b58158e2bee20d02d4c94ecdbf87c4afd8c21

commit r17-2491-g230b58158e2bee20d02d4c94ecdbf87c4afd8c21
Author: Lewis Hyatt <[email protected]>
Date:   Sat Jul 11 14:21:12 2026 -0400

    testsuite: Add { dg-lto-do incr-link } option
    
    Similar to { dg-lto-do ar-link }, which allows testing the combination of
    multiple LTO objects into an archive before linking, this new directive
    allows testing the incremental linking modes of the LTO front end.
    
    gcc/ChangeLog:
    
            * doc/sourcebuild.texi: Document ar-link and incr-link options to
            dg-lto-do directive.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/lto/README: Update to document ar-link and incr-link.
            * lib/lto.exp: Support incr-link directive throughout.

Diff:
---
 gcc/doc/sourcebuild.texi        |  9 ++++++++-
 gcc/testsuite/gcc.dg/lto/README | 17 ++++++++++-------
 gcc/testsuite/lib/lto.exp       | 41 ++++++++++++++++++++++++++++++-----------
 3 files changed, 48 insertions(+), 19 deletions(-)

diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 6c0a3a4c74f9..31265ddd28b3 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -4119,12 +4119,19 @@ it is executed.  It is one of:
 Compile with @option{-c} to produce a relocatable object file.
 @item link
 Compile, assemble, and link to produce an executable file.
+@item ar-link
+Similar to @code{link}, but combine all but the first source file into
+an archive file before the final link.
+@item incr-link
+As with @code{ar-link}, but combine the files into an object file
+using incremental linking, rather than an archive file.  This enables
+testing the incremental linking features of the LTO front end.
 @item run
 Produce and run an executable file, which is expected to return
 an exit code of 0.
 @end table
 
-The default is @code{assemble}.  That can be overridden for a set of
+The default is @code{run}.  That can be overridden for a set of
 tests by redefining @code{dg-do-what-default} within the @code{.exp}
 file for those tests.
 
diff --git a/gcc/testsuite/gcc.dg/lto/README b/gcc/testsuite/gcc.dg/lto/README
index 1ee8b00dee8f..04c05a2ee1d0 100644
--- a/gcc/testsuite/gcc.dg/lto/README
+++ b/gcc/testsuite/gcc.dg/lto/README
@@ -44,12 +44,15 @@ where there is a single file named 'foo_0.C'.
 
 === The dg-lto-do Directive ==
 
-The only supported dg-lto-do options are 'assemble', 'run' and 'link'.
-Additionally, these can only be used in the main file.  If
-'assemble' is used, only the individual object files are
-generated.  If 'link' is used, the final executable is generated
-but not executed (in this case, function main() needs to exist
-but it does not need to do anything).  If 'run' is used, the
-final executable is generated and the resulting binary executed.
+The supported dg-lto-do options are 'assemble', 'run', 'link', 'ar-link',
+and 'incr-link'.  This option can only be used in the main file.  If
+'assemble' is used, only the individual object files are generated.  If
+'link' is used, the final executable is generated but not executed (in
+this case, function main() needs to exist but it does not need to do
+anything).  If 'run' is used, the final executable is generated and the
+resulting binary executed.  'ar-link' and 'incr-link' are similar to
+'link', except that the non-main object files are combined together before
+the final link, into either an archive, in the former case, or an object
+file via incremental linking, in the latter.
 
 The default value for dg-lto-do is 'run'.
diff --git a/gcc/testsuite/lib/lto.exp b/gcc/testsuite/lib/lto.exp
index 2cff54b699d0..7243547a52d8 100644
--- a/gcc/testsuite/lib/lto.exp
+++ b/gcc/testsuite/lib/lto.exp
@@ -417,7 +417,9 @@ proc lto-link-and-maybe-run { testname objlist dest optall optfile optstr } {
     }
 
     # Check for diagnostics specified by directives
-    set comp_output [lto_handle_diagnostics $comp_output $optstr]
+    if { ! [string equal "incr-link" $optstr] } {
+	set comp_output [lto_handle_diagnostics $comp_output $optstr]
+    }
 
     # Prune unimportant visibility warnings before checking output.
     set comp_output [lto_prune_warns $comp_output]
@@ -432,7 +434,8 @@ proc lto-link-and-maybe-run { testname objlist dest optall optfile optstr } {
 
     # Return if we only needed to link.
     if { ![string compare "link" $compile_type] \
-        || ![string compare "ar-link" $compile_type] } {
+        || ![string compare "ar-link" $compile_type] \
+        || ![string compare "incr-link" $compile_type] } {
 	return
     }
 
@@ -578,6 +581,8 @@ proc lto-get-options-main { src } {
 		set compile_type "link"
 	    } elseif { ![string compare "ar-link" $dgdo] } {
 		set compile_type "ar-link"
+	    } elseif { ![string compare "incr-link" $dgdo] } {
+		set compile_type "incr-link"
 	    } else {
 		warning "lto.exp does not support dg-lto-do $dgdo"
 	    }
@@ -772,8 +777,12 @@ proc lto-execute-1 { src1 sid } {
 
     # The test needs to build all but the main file into an archive and then
     # link them all together.
-    if { ![string compare "ar-link" $compile_type] } {
+    set is_incr_link [string equal "incr-link" $compile_type]
+    set is_ar_link [string equal "ar-link" $compile_type]
+    if { $is_ar_link } {
         set arname "${sid}_${base}.a"
+    } elseif { $is_incr_link } {
+        set arname "${sid}_${base}.o"
     }
 
     # Remove the $srcdir and $tmpdir prefixes from $src1.  (It would
@@ -842,13 +851,20 @@ proc lto-execute-1 { src1 sid } {
 
 	# Bundle all but the main file into an archive. Update objlist to only
 	# have the archive and the last file.
-	if { ![string compare "ar-link" $compile_type] } {
+	# Only attempt the incr-link mode if the linker plugin is explicitly in use.
+	set sav_compile_type $compile_type
+	set sav_obj_list $obj_list
+	if { $is_incr_link && [lsearch -exact $option "-fuse-linker-plugin"] < 0 } {
+	    set compile_type "link"
+	} elseif { $is_incr_link || $is_ar_link } {
 	    set mainsrc [lindex $obj_list 0]
 	    set obj_list [lrange $obj_list 1 end]
-	    lto-build-archive \
-		"[lindex $obj_list 1]-[lindex $obj_list end]" \
-		$obj_list $arname
-
+	    set testname "[lindex $obj_list 1]-[lindex $obj_list end]"
+	    if { $is_incr_link } {
+		lto-link-and-maybe-run $testname $obj_list $arname "-r" "" "incr-link"
+	    } else {
+		lto-build-archive $testname $obj_list $arname
+	    }
 	    set obj_list ""
 	    lappend obj_list $mainsrc
 	    lappend obj_list $arname
@@ -857,7 +873,7 @@ proc lto-execute-1 { src1 sid } {
 
 	# Link (using the compiler under test), run, and clean up tests.
 	if { ![string compare "run" $compile_type] \
-	     || ![string compare "ar-link" $compile_type] \
+	     || $is_ar_link || $is_incr_link \
 	     || ![string compare "link" $compile_type] } {
 
 	    # Filter out any link options we were asked to suppress.
@@ -874,7 +890,7 @@ proc lto-execute-1 { src1 sid } {
 		$obj_list $execname $filtered "${additional-flags} ${dg-extra-ld-options}" \
 		    $filtered
 
-	    if (![string compare "ar-link" $compile_type]) {
+	    if { $is_ar_link || $is_incr_link } {
 		file_on_host delete $arname
 	      }
 	}
@@ -923,7 +939,7 @@ proc lto-execute-1 { src1 sid } {
 	unset testname_with_flags
 	
 	if { ![string compare "run" $compile_type] \
-	     || ![string compare "ar-link" $compile_type] \
+	     || $is_ar_link || $is_incr_link \
 	     || ![string compare "link" $compile_type] } {
 	    file_on_host delete $execname
 	}
@@ -931,6 +947,9 @@ proc lto-execute-1 { src1 sid } {
 	if {$sid eq "f_lto"} {
 	    cleanup-modules ""
 	}
+
+	set compile_type $sav_compile_type
+	set obj_list $sav_obj_list
     }
 }