diff --git a/.github/workflows/compare_pr_to_master.v b/.github/workflows/compare_pr_to_master.v
index 89ef3e92e3..c1c151d340 100755
--- a/.github/workflows/compare_pr_to_master.v
+++ b/.github/workflows/compare_pr_to_master.v
@@ -31,67 +31,113 @@ fn xtime(cmd string) {
 	}
 }
 
+fn show_size(fpath string) {
+	println('>Size of ${fpath:20s}: ${os.file_size(fpath):10}')
+}
+
+fn compare_size(fpath1 string, fpath2 string) {
+	size1 := os.file_size(fpath1)
+	size2 := os.file_size(fpath2)
+	diff_ := size2 - size1
+	println('>>>>>> size("${fpath2:15}") - size("${fpath1:15}") = ${size2:10} - ${size1:10} = ${diff_:10}')
+}
+
 fn vcompare(vold string, vnew string) {
-	println('>Size of ${vold}: ${os.file_size(vold)}')
-	println('>Size of ${vnew}: ${os.file_size(vnew)}')
+	r("v repeat --nmaxs 7 -R 3 '${vold} -check-syntax           examples/hello_world.v' '${vnew} -check-syntax           examples/hello_world.v'")
+	r("v repeat --nmaxs 7 -R 3 '${vold} -check                  examples/hello_world.v' '${vnew} -check                  examples/hello_world.v'")
+	r("v repeat --nmaxs 7 -R 3 '${vold} -no-parallel -o ohw.c   examples/hello_world.v' '${vnew} -no-parallel -o nhw.c   examples/hello_world.v'")
+	compare_size('ohw.c', 'nhw.c')
+	r("v repeat --nmaxs 7 -R 3 '${vold} -no-parallel -o ohw.exe examples/hello_world.v' '${vnew} -no-parallel -o nhw.exe examples/hello_world.v'")
+	compare_size('ohw.exe', 'nhw.exe')
 
-	r("v repeat --nmaxs 7 -R 3 '${vold} -check-syntax examples/hello_world.v' '${vnew} -check-syntax examples/hello_world.v'")
-	r("v repeat --nmaxs 7 -R 3 '${vold} -check        examples/hello_world.v' '${vnew} -check        examples/hello_world.v'")
-	r("v repeat --nmaxs 7 -R 3 '${vold} -o  ohw.c     examples/hello_world.v' '${vnew} -o  nhw.c     examples/hello_world.v'")
-	println('>Size of ohw.c: ${os.file_size('ohw.c')}')
-	println('>Size of nhw.c: ${os.file_size('nhw.c')}')
-	r("v repeat --nmaxs 7 -R 3 '${vold} -o  ohw.exe   examples/hello_world.v' '${vnew} -o  nhw.exe   examples/hello_world.v'")
-	println('>Size of ohw.exe: ${os.file_size('ohw.exe')}')
-	println('>Size of nhw.exe: ${os.file_size('nhw.exe')}')
+	r("v repeat --nmaxs 7 -R 3 '${vold} -check-syntax cmd/v'          '${vnew} -check-syntax          cmd/v'")
+	r("v repeat --nmaxs 7 -R 3 '${vold} -check        cmd/v'          '${vnew} -check                 cmd/v'")
+	r("v repeat --nmaxs 7 -R 3 '${vold} -no-parallel -o ov.c   cmd/v' '${vnew} -no-parallel -o nv.c   cmd/v'")
+	compare_size('ov.c', 'nv.c')
+	r("v repeat --nmaxs 7 -R 3 '${vold} -no-parallel -o ov.exe cmd/v' '${vnew} -no-parallel -o nv.exe cmd/v'")
+	compare_size('ov.exe', 'nv.exe')
+}
 
-	r("v repeat --nmaxs 7 -R 3 '${vold} -check-syntax cmd/v'                  '${vnew} -check-syntax cmd/v'")
-	r("v repeat --nmaxs 7 -R 3 '${vold} -check        cmd/v'                  '${vnew} -check        cmd/v'")
-	r("v repeat --nmaxs 7 -R 3 '${vold} -o  ov.c      cmd/v'                  '${vnew} -o  nv.c      cmd/v'")
-	println('>Size of ov.c: ${os.file_size('ov.c')}')
-	println('>Size of nv.c: ${os.file_size('nv.c')}')
-	r("v repeat --nmaxs 7 -R 3 '${vold} -o  ov.exe    cmd/v'                  '${vnew} -o  nv.exe    cmd/v'")
-	println('>Size of ov.exe: ${os.file_size('ov.exe')}')
-	println('>Size of nv.exe: ${os.file_size('nv.exe')}')
-
-	// After all the measurements are done, delete all the generated temporary files,
-	// except the `vold` and `vnew` compilers, so that they can be used later in manual
-	// experiments:
-	r('rm -rf ohw* nhw* nv* ov*')
+fn hline(header_message string) {
+	println('='.repeat(98))
+	println(header_message)
 }
 
 fn main() {
-	start := time.now()
 	// The starting point, when this program should be started, is just after `gh pr checkout NUMBER`.
+	start := time.now()
+
 	pr_branch := gbranch()
-	println('Current git branch: ${pr_branch}, commit: ${gcommit()}')
+	hline('Current git branch: ${pr_branch}, commit: ${gcommit()}')
 	println('    Compiling new V executables from PR branch: ${pr_branch}, commit: ${gcommit()} ...')
 	// *not* using v self here is deliberate, so that the `v` executable itself, is not changed after running this script
 	xtime('./v     -o vnew1 cmd/v')
 	xtime('./vnew1 -o vnew2 cmd/v')
-	xtime('./vnew2 -o vnew  cmd/v')
-	r('rm -rf vnew1 vnew2')
+	xtime('./vnew2 -no-parallel -o vnew  cmd/v')
+	xtime('./vnew -no-parallel -o nhw_current.c examples/hello_world.v')
+	xtime('./vnew -no-parallel -o nv_current.c cmd/v')
 	if compare_prod {
-		xtime('./vnew -prod -o vnew_prod cmd/v')
+		xtime('./vnew -no-parallel -prod -o vnew_prod cmd/v')
 	}
+	show_size('nhw_current.c')
+	show_size('nv_current.c')
+	show_size('vnew')
+	if compare_prod {
+		show_size('vnew_prod')
+	}
+	r('rm -rf vnew1 vnew2')
 
 	r('git checkout master')
 	master_branch := gbranch()
-	println('    Compiling old V executables from branch: ${master_branch}, commit: ${gcommit()} ...')
+	hline('    Compiling old V executables from branch: ${master_branch}, commit: ${gcommit()} ...')
 	xtime('./v     -o vold1 cmd/v')
 	xtime('./vold1 -o vold2 cmd/v')
-	xtime('./vold2 -o vold  cmd/v')
-	r('rm -rf vold1 vold2')
+	xtime('./vold2 -no-parallel -o vold  cmd/v')
+	xtime('./vnew -no-parallel -o ohw_master.c examples/hello_world.v')
+	xtime('./vold -no-parallel -o ov_master.c  cmd/v')
 	if compare_prod {
-		xtime('./vold -prod -o vold_prod cmd/v')
+		xtime('./vold -no-parallel -prod -o vold_prod cmd/v')
+		show_size('vold_prod')
 	}
+	show_size('ohw_master.c')
+	show_size('ov_master.c')
+	show_size('vold')
+	if compare_prod {
+		show_size('vold_prod')
+	}
+	r('rm -rf vold1 vold2')
 
-	r('git checkout ${pr_branch}') // we are on the PR branch again
+	hline('File sizes so far ...')
+	compare_size('ohw_master.c', 'nhw_current.c')
+	compare_size('ov_master.c', 'nv_current.c')
+	compare_size('vold', 'vnew')
 
-	println('    Measuring at PR branch: ${pr_branch}, commit: ${gcommit()} ...')
+	r('git checkout ${pr_branch}')
+	// we are on the PR branch again
+	hline('    Measuring at PR branch: ${pr_branch}, commit: ${gcommit()} ...')
 	if compare_prod {
 		vcompare('./vold_prod', './vnew_prod')
 	} else {
 		vcompare('./vold', './vnew')
 	}
 	println('Done. Total time: ${(time.now() - start).seconds()} s.')
+
+	hline('Final summary for file diff sizes on their own branches:')
+	compare_size('ohw_master.c', 'nhw_current.c')
+	compare_size('ov_master.c', 'nv_current.c')
+	compare_size('vold', 'vnew')
+	if compare_prod {
+		compare_size('vold_prod', 'vnew_prod')
+	}
+
+	hline('Final summary for file diff sizes for generated files on the *current* branch:')
+	compare_size('ohw.c', 'nhw.c')
+	compare_size('ov.c', 'nv.c')
+	compare_size('ohw.exe', 'nhw.exe')
+	compare_size('ov.exe', 'nv.exe')
+
+	// After all the measurements are done, delete all the generated temporary files,
+	// except the `vold` and `vnew` compilers, so that they can be used later in manual
+	// experiments:
+	r('rm -rf ohw* nhw* nv* ov*')
 }