[Support] Speedup llvm-dwarfdump 3.9x

Currently `strace llvm-dwarfdump x.debug >/tmp/file`:

  ioctl(1, TCGETS, 0x7ffd64d7f340)        = -1 ENOTTY (Inappropriate ioctl for device)
  write(1, "           DW_AT_decl_line\t(89)\n"..., 4096) = 4096
  ioctl(1, TCGETS, 0x7ffd64d7f400)        = -1 ENOTTY (Inappropriate ioctl for device)
  ioctl(1, TCGETS, 0x7ffd64d7f410)        = -1 ENOTTY (Inappropriate ioctl for device)
  ioctl(1, TCGETS, 0x7ffd64d7f400)        = -1 ENOTTY (Inappropriate ioctl for device)

After this patch:

  write(1, "0000000000001102 \"strlen\")\n     "..., 4096) = 4096
  write(1, "site\n                  DW_AT_low"..., 4096) = 4096
  write(1, "d53)\n\n0x000e4d4d:       DW_TAG_G"..., 4096) = 4096

The same speedup can be achieved by `--color=0` but that is not much convenient.

This implementation has been suggested by Joerg Sonnenberger.

Differential Revision: https://reviews.llvm.org/D86406

diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h
index e9c710d..cae5743 100644 (file)
--- a/llvm/include/llvm/Support/raw_ostream.h
+++ b/llvm/include/llvm/Support/raw_ostream.h
@@ -412,6 +412,7 @@ class raw_fd_ostream : public raw_pwrite_stream {
   int FD;
   bool ShouldClose;
   bool SupportsSeeking = false;
+  mutable Optional<bool> HasColors;
 
 #ifdef _WIN32
   /// True if this fd refers to a Windows console device. Mintty and other

diff --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp
index 86c4899..83050c8 100644 (file)
--- a/llvm/lib/Support/raw_ostream.cpp
+++ b/llvm/lib/Support/raw_ostream.cpp
@@ -858,7 +858,9 @@ bool raw_fd_ostream::is_displayed() const {
 }
 
 bool raw_fd_ostream::has_colors() const {
-  return sys::Process::FileDescriptorHasColors(FD);
+  if (!HasColors)
+    HasColors = sys::Process::FileDescriptorHasColors(FD);
+  return *HasColors;
 }
 
 Expected<sys::fs::FileLocker> raw_fd_ostream::lock() {