Remove -debug-time-compilation

This flag no longer does anything now that the unified statistics
reporting infrastructure exists. It is better to use
-driver-time-compilation to see a bird's eye view of timing statistics
for frontend jobs, and -stats-output-dir to see a down-and-dirty view of
everything including performance counters.

Author: CodaFi

docs/CompilerPerformance.md

@@ -559,30 +559,6 @@ compilers on hand while you're working.
        0.0001 (100.0%)   0.0001 (100.0%)   0.0001 (100.0%)   0.0490 (100.0%)  Total
     ```
 
-  - `-Xfrontend -debug-time-compilation`: asks each frontend to print out timers
-    for each phase of its execution. Its output (per-frontend) looks like this:
-
-    ```
-    ===-------------------------------------------------------------------------===
-                                 Swift compilation
-    ===-------------------------------------------------------------------------===
-    Total Execution Time: 0.0876 seconds (0.0877 wall clock)
-
-     ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
-     0.0241 ( 53.9%)   0.0394 ( 92.0%)   0.0635 ( 72.5%)   0.0635 ( 72.5%)  Import resolution
-     0.0170 ( 38.0%)   0.0025 (  5.8%)   0.0195 ( 22.3%)   0.0195 ( 22.2%)  Type checking / Semantic analysis
-     0.0013 (  3.0%)   0.0004 (  0.8%)   0.0017 (  1.9%)   0.0017 (  1.9%)  LLVM output
-     0.0010 (  2.3%)   0.0003 (  0.7%)   0.0013 (  1.5%)   0.0013 (  1.5%)  SILGen
-     0.0006 (  1.4%)   0.0002 (  0.4%)   0.0008 (  0.9%)   0.0008 (  0.9%)  IRGen
-     0.0004 (  0.8%)   0.0000 (  0.1%)   0.0004 (  0.5%)   0.0004 (  0.5%)  SIL optimization
-     0.0002 (  0.5%)   0.0001 (  0.1%)   0.0003 (  0.3%)   0.0003 (  0.3%)  LLVM optimization
-     0.0001 (  0.1%)   0.0000 (  0.1%)   0.0001 (  0.1%)   0.0001 (  0.1%)  Parsing
-     0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)  SIL verification (pre-optimization)
-     0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)  SIL verification (post-optimization)
-     0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)  AST verification
-     0.0448 (100.0%)   0.0428 (100.0%)   0.0876 (100.0%)   0.0877 (100.0%)  Total
-    ```
-
   - `-Xfrontend -debug-time-function-bodies`: asks each frontend to print out
     the time spent typechecking _every function_ in the program, sorted by time
     taken. The output is therefore voluminous, but can help when reducing a
@@ -1053,10 +1029,8 @@ getting slower between versions:
      parameter of the script). Reconfirm that _just those two isolated frontend
      processes_ still show the regression you're interested in isolating.
 
-  6. Check high-level diagnostic output between the two compilers, either the
-     newer unified stats reporter (`-stats-output-dir`) or the older flags
-     (`-Xfrontend -debug-time-compilation` and friends). Comparing the two will
-     often guide the search.
+  6. Check the value of performance counters between the two compilers via the
+     unified stats reporter (`-stats-output-dir`).
 
   7. Run both frontend processes under a profiler and compare the profiles in
      detail. At this point there ought to be _some_ sign of a difference, either

include/swift/Frontend/FrontendOptions.h

@@ -161,12 +161,6 @@ class FrontendOptions {
   /// If set, dumps wall time taken to check each expression.
   bool DebugTimeExpressionTypeChecking = false;
 
-  /// If set, prints the time taken in each major compilation phase to 
-  /// llvm::errs().
-  ///
-  /// \sa swift::SharedTimer
-  bool DebugTimeCompilation = false;
-
   /// The path to which we should output statistics files.
   std::string StatsOutputDir;
 

include/swift/Option/FrontendOptions.td

@@ -259,8 +259,6 @@ def build_request_dependency_graph : Flag<["-"], "build-request-dependency-graph
 def output_request_graphviz : Separate<["-"], "output-request-graphviz">,
   HelpText<"Emit GraphViz output visualizing the request dependency graph">;
 
-def debug_time_compilation : Flag<["-"], "debug-time-compilation">,
-  HelpText<"Prints the time taken by each compilation phase">;
 def debug_time_function_bodies : Flag<["-"], "debug-time-function-bodies">,
   HelpText<"Dumps the time it takes to type-check each function body">;
 def debug_time_expression_type_checking : Flag<["-"], "debug-time-expression-type-checking">,

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -234,8 +234,6 @@ void ArgsToFrontendOptionsConverter::computePrintStatsOptions() {
 
 void ArgsToFrontendOptionsConverter::computeDebugTimeOptions() {
   using namespace options;
-  Opts.DebugTimeCompilation |= Args.hasArg(OPT_debug_time_compilation);
-
   if (const Arg *A = Args.getLastArg(OPT_stats_output_dir)) {
     Opts.StatsOutputDir = A->getValue();
     if (Args.getLastArg(OPT_trace_stats_events)) {

lib/FrontendTool/FrontendTool.cpp

@@ -2232,9 +2232,6 @@ int swift::performFrontend(ArrayRef<const char *> Args,
   PDC.setFormattingStyle(
       Invocation.getDiagnosticOptions().PrintedFormattingStyle);
 
-  if (Invocation.getFrontendOptions().DebugTimeCompilation)
-    SharedTimer::enableCompilationTimers();
-
   if (Invocation.getFrontendOptions().PrintStats) {
     llvm::EnableStatistics();
   }