From 3e4544025d664fe381be96bf2526f08b7464e3cb Mon Sep 17 00:00:00 2001
From: Alex Wang <aw1621107@gmail.com>
Date: Sat, 24 Sep 2016 23:56:54 -0400
Subject: [PATCH] Prefer brewed Clang over gcc-6 for needs :openmp

Clang has fully implemented OpenMP support as of LLVM 3.7, so if OpenMP
is required by a formula gcc is no longer the only choice of compiler.

Clang should be preferred over gcc because using gcc meant linking
against libstdc++, which is ABI incompatible with libc++. This may be
unnoticeable for some users, but it causes other builds to fail, e.g.
pstoedit when imagemagick was built with OpenMP. pstoedit is required
for the octave formula, so for some users this could be a significant
problem.
---
 Library/Homebrew/compilers.rb             | 9 +++++----
 Library/Homebrew/development_tools.rb     | 7 +++++++
 Library/Homebrew/shims/super/cc           | 6 +++++-
 Library/Homebrew/shims/super/llvm_clang   | 1 +
 Library/Homebrew/shims/super/llvm_clang++ | 1 +
 5 files changed, 19 insertions(+), 5 deletions(-)
 create mode 120000 Library/Homebrew/shims/super/llvm_clang
 create mode 120000 Library/Homebrew/shims/super/llvm_clang++

diff --git a/Library/Homebrew/compilers.rb b/Library/Homebrew/compilers.rb
index fdfcab817b..9ee847db0e 100644
--- a/Library/Homebrew/compilers.rb
+++ b/Library/Homebrew/compilers.rb
@@ -3,9 +3,10 @@ module CompilerConstants
   GNU_GCC_VERSIONS = %w[4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 6 7].freeze
   GNU_GCC_REGEXP = /^gcc-(4\.[3-9]|[5-7])$/
   COMPILER_SYMBOL_MAP = {
-    "gcc-4.0"  => :gcc_4_0,
-    "gcc-4.2"  => :gcc,
-    "clang"    => :clang,
+    "gcc-4.0"    => :gcc_4_0,
+    "gcc-4.2"    => :gcc,
+    "clang"      => :clang,
+    "llvm_clang" => :llvm_clang,
   }.freeze
 
   COMPILERS = COMPILER_SYMBOL_MAP.values +
@@ -86,7 +87,7 @@ class CompilerSelector
   Compiler = Struct.new(:name, :version)
 
   COMPILER_PRIORITY = {
-    clang: [:clang, :gcc, :gnu, :gcc_4_0],
+    clang: [:clang, :gcc, :gnu, :gcc_4_0, :llvm_clang],
     gcc: [:gcc, :gnu, :clang, :gcc_4_0],
     gcc_4_0: [:gcc_4_0, :gcc, :gnu, :clang],
   }.freeze
diff --git a/Library/Homebrew/development_tools.rb b/Library/Homebrew/development_tools.rb
index 62f9b3d71e..d081067a84 100644
--- a/Library/Homebrew/development_tools.rb
+++ b/Library/Homebrew/development_tools.rb
@@ -86,6 +86,13 @@ class DevelopmentTools
         end
     end
 
+    def llvm_clang_build_version
+      @llvm_clang_build_version ||= if Tab.for_name "llvm"
+        path = Formulary.factory("llvm").opt_prefix/"bin/clang"
+        `#{path} --version`[/clang version (\d\.\d\.\d)/, 1]
+      end
+    end
+
     def non_apple_gcc_version(cc)
       (@non_apple_gcc_version ||= {}).fetch(cc) do
         path = HOMEBREW_PREFIX.join("opt", "gcc", "bin", cc)
diff --git a/Library/Homebrew/shims/super/cc b/Library/Homebrew/shims/super/cc
index 1552f412d4..167fe8c21d 100755
--- a/Library/Homebrew/shims/super/cc
+++ b/Library/Homebrew/shims/super/cc
@@ -58,6 +58,8 @@ class Cmd
     @tool ||= case @arg0
     when "ld" then "ld"
     when "cpp" then "cpp"
+    when /llvm_(clang(\+\+)?)/
+     "#{ENV["HOMEBREW_PREFIX"]}/opt/llvm/bin/#{$1}"
     when /\w\+\+(-\d(\.\d)?)?$/
       case ENV["HOMEBREW_CC"]
       when /clang/
@@ -154,7 +156,7 @@ class Cmd
       /^-O[0-9zs]?$/, "-fast", "-no-cpp-precomp",
       "-pedantic", "-pedantic-errors", "-Wno-long-double",
       "-Wno-unused-but-set-variable"
-    when "-fopenmp", "-lgomp", "-mno-fused-madd", "-fforce-addr", "-fno-defer-pop",
+    when "-mno-fused-madd", "-fforce-addr", "-fno-defer-pop",
       "-mno-dynamic-no-pic", "-fearly-inlining", /^-f(?:no-)?inline-functions-called-once/,
       /^-finline-limit/, /^-f(?:no-)?check-new/, "-fno-delete-null-pointer-checks",
       "-fcaller-saves", "-fthread-jumps", "-fno-reorder-blocks", "-fcse-skip-blocks",
@@ -163,6 +165,8 @@ class Cmd
       "-fuse-linker-plugin", "-frounding-math"
       # clang doesn't support these flags
       args << arg unless tool =~ /^clang/
+    when "-fopenmp", "-lgomp"
+      args << arg if tool =~ /^llvm_clang/
     when "--fast-math"
       arg = "-ffast-math" if tool =~ /^clang/
       args << arg
diff --git a/Library/Homebrew/shims/super/llvm_clang b/Library/Homebrew/shims/super/llvm_clang
new file mode 120000
index 0000000000..2652f5f42c
--- /dev/null
+++ b/Library/Homebrew/shims/super/llvm_clang
@@ -0,0 +1 @@
+cc
\ No newline at end of file
diff --git a/Library/Homebrew/shims/super/llvm_clang++ b/Library/Homebrew/shims/super/llvm_clang++
new file mode 120000
index 0000000000..2652f5f42c
--- /dev/null
+++ b/Library/Homebrew/shims/super/llvm_clang++
@@ -0,0 +1 @@
+cc
\ No newline at end of file