[clang-format][NFC] Skip unneeded calculations

[HazardyKnusperkeks]

Summary

For UT_Never the remaining results of the max() function are not needed, introduce a fast path for UT_Never.

[owenpan]

clang/lib/Format/WhitespaceManager.cpp

1433–1440

So that we don't have to worry about signed vs unsigned.

1434–1436

Doing this would lose some of the abstraction we have now without any gain in performance? Then we should leave it (and appendIndentText below) as is.

[HazardyKnusperkeks]

clang/lib/Format/WhitespaceManager.cpp

1434–1436

The UT_Never case would be faster, if that would be measurable I don't know.

[owenpan]

clang/lib/Format/WhitespaceManager.cpp

1434–1436

Probably negligible. Can we keep the current code which encapsulates the handling of UT_Never within appendIndentText?

[HazardyKnusperkeks]

Reverted the changes in the switch. We now only have a fast path.

On my machine 4 consecutive runs of the clang format unittests, the last three times (as reported by gtest) are:

	Before patch	After Patch
Run 1	12769ms	12535ms
Run 2	13703ms	12456ms
Run 3	13305ms	12470ms
Avg	13259ms	12487ms

That would be 6% speedup, more than I'd excpected.

Release Build 32 Bit Windows.

[owenpan]

I ran (on macOS Ventura) the release build of clang-format 8627811 on the entire clang codebase and saw only a 0.12% reduction in runtime, which is what I expected.

	Run 1	Run 2	Run 3	Average
w/o patch	50.107s	50.082s	50.120s	50.103s
w/ patch	50.031s	49.998s	50.094s	50.041s

[owenpan]

To my surprise, tools/clang/unittests/Format/FormatTests with the patch ran a little bit slower:

	Run 1	Run 2	Run 3	Average
w/o patch	2707ms	2697ms	2710ms	2705ms
w/ patch	2720ms	2719ms	2724ms	2721ms

[owenpan]

The refactoring std::max(0, C.Spaces) part still looks good though, but probably it's not worth it to have a patch just for that.

clang/lib/Format/WhitespaceManager.cpp

if (C.CreateReplacement) {
         appendEscapedNewlineText(ReplacementText, C.NewlinesBefore,
                                  C.PreviousEndOfTokenColumn,
                                  C.EscapedNewlineColumn);
       } else {
         appendNewlineText(ReplacementText, C.NewlinesBefore);
       }
       // FIXME: This assert should hold if we computed the column correctly.
       // assert((int)C.StartOfTokenColumn >= C.Spaces);
-      appendIndentText(
-          ReplacementText, C.Tok->IndentLevel, std::max(0, C.Spaces),
-          std::max((int)C.StartOfTokenColumn, C.Spaces) - std::max(0, C.Spaces),
+      unsigned Spaces = std::max(0, C.Spaces);
+      if (Style.UseTab == FormatStyle::UT_Never) {
+        ReplacementText.append(Spaces, ' ');
+      } else {
+        appendIndentText(ReplacementText, C.Tok->IndentLevel, Spaces,
+                         std::max((int)C.StartOfTokenColumn, C.Spaces) - Spaces,
                          C.IsAligned);
+      }
       ReplacementText.append(C.CurrentLinePrefix);
       storeReplacement(C.OriginalWhitespaceRange, ReplacementText);
     }
   }
 }
 
 void WhitespaceManager::storeReplacement(SourceRange Range, StringRef Text) {
   unsigned WhitespaceLength = SourceMgr.getFileOffset(Range.getEnd()) -