Do not optimize for host CPU by default.

GitHub: Fixes #323.

driver/target.cpp

@@ -6,8 +6,15 @@
 // file for details.
 //
 //===----------------------------------------------------------------------===//
+//
+// Note: The target CPU detection logic has been adapted from Clang
+// (lib/Driver/Tools.cpp).
+//
+//===----------------------------------------------------------------------===//
 
 #include "driver/target.h"
+#include "gen/llvmcompat.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -16,6 +23,57 @@
 #include "llvm/Target/TargetOptions.h"
 #include "mars.h"
 
+
+static std::string getX86TargetCPU(std::string arch,
+    const llvm::Triple &triple)
+{
+    if (!arch.empty()) {
+        if (arch != "native")
+          return arch;
+
+        // FIXME: Reject attempts to use -march=native unless the target matches
+        // the host.
+        //
+        // FIXME: We should also incorporate the detected target features for use
+        // with -native.
+        std::string cpu = llvm::sys::getHostCPUName();
+        if (!cpu.empty() && cpu != "generic")
+          return cpu;
+    }
+
+    // Select the default CPU if none was given (or detection failed).
+
+    bool is64Bit = triple.getArch() == llvm::Triple::x86_64;
+
+    if (triple.isOSDarwin())
+        return is64Bit ? "core2" : "yonah";
+
+    // Everything else goes to x86-64 in 64-bit mode.
+    if (is64Bit)
+        return "x86-64";
+
+    if (triple.getOSName().startswith("haiku"))
+        return "i586";
+    if (triple.getOSName().startswith("openbsd"))
+        return "i486";
+    if (triple.getOSName().startswith("bitrig"))
+        return "i686";
+    if (triple.getOSName().startswith("freebsd"))
+        return "i486";
+    if (triple.getOSName().startswith("netbsd"))
+        return "i486";
+#if LDC_LLVM_VER >= 302
+    // All x86 devices running Android have core2 as their common
+    // denominator. This makes a better choice than pentium4.
+    if (triple.getEnvironment() == llvm::Triple::Android)
+        return "core2";
+#endif
+
+    // Fallback to p4.
+    return "pentium4";
+}
+
+
 llvm::TargetMachine* createTargetMachine(
     std::string targetTriple,
     std::string arch,
@@ -46,7 +104,7 @@ llvm::TargetMachine* createTargetMachine(
 #endif
     }
 
-    std::string triple;
+    llvm::Triple triple;
 
     // did the user override the target triple?
     if (targetTriple.empty())
@@ -56,21 +114,20 @@ llvm::TargetMachine* createTargetMachine(
             error("you must specify a target triple as well with -mtriple when using the -arch option");
             fatal();
         }
-        triple = defaultTriple;
+        triple = llvm::Triple(defaultTriple);
     }
     else
     {
-        triple = llvm::Triple::normalize(targetTriple);
+        triple = llvm::Triple(llvm::Triple::normalize(targetTriple));
     }
 
-
     // Allocate target machine.
     const llvm::Target *theTarget = NULL;
     // Check whether the user has explicitly specified an architecture to compile for.
     if (arch.empty())
     {
         std::string Err;
-        theTarget = llvm::TargetRegistry::lookupTarget(triple, Err);
+        theTarget = llvm::TargetRegistry::lookupTarget(triple.str(), Err);
         if (theTarget == 0)
         {
             error("%s Please use the -march option.", Err.c_str());
@@ -96,6 +153,19 @@ llvm::TargetMachine* createTargetMachine(
         }
     }
 
+
+    // With an empty CPU string, LLVM will default to the host CPU, which is
+    // usually not what we want (expected behavior from other compilers is
+    // to default to "generic").
+    if (cpu.empty())
+    {
+        if (triple.getArch() == llvm::Triple::x86_64 ||
+            triple.getArch() == llvm::Triple::x86)
+        {
+            cpu = getX86TargetCPU(arch, triple);
+        }
+    }
+
     // Package up features to be passed to target/subtarget
     std::string FeaturesStr;
     if (cpu.size() || attrs.size())
@@ -109,14 +179,14 @@ llvm::TargetMachine* createTargetMachine(
 #if LDC_LLVM_VER == 300
     llvm::NoFramePointerElim = genDebugInfo;
 
-    return theTarget->createTargetMachine(triple, cpu, FeaturesStr,
+    return theTarget->createTargetMachine(triple.str(), cpu, FeaturesStr,
         relocModel, codeModel);
 #else
     llvm::TargetOptions targetOptions;
     targetOptions.NoFramePointerElim = genDebugInfo;
 
     return theTarget->createTargetMachine(
-        triple,
+        triple.str(),
         cpu,
         FeaturesStr,
         targetOptions,