[X86] Add 'sahf' CPU feature to frontend

Summary:
Make clang accept `-msahf` (and `-mno-sahf`) flags to activate the
`+sahf` feature for the backend, for bug 36028 (Incorrect use of
pushf/popf enables/disables interrupts on amd64 kernels).  This was
originally submitted in bug 36037 by Jonathan Looney
<jonlooney@gmail.com>.

As described there, GCC also uses `-msahf` for this feature, and the
backend already recognizes the `+sahf` feature. All that is needed is to
teach clang to pass this on to the backend.

The mapping of feature support onto CPUs may not be complete; rather, it
was chosen to match LLVM's idea of which CPUs support this feature (see
lib/Target/X86/X86.td).

I also updated the affected test case (CodeGen/attr-target-x86.c) to
match the emitted output.

Reviewers: craig.topper, coby, efriedma, rsmith

Reviewed By: craig.topper

Subscribers: emaste, cfe-commits

Differential Revision: https://reviews.llvm.org/D43394

llvm-svn: 325446

2 files changed, 12 insertions, 0 deletions

diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp
index 5f9f6bb2f05..f3ebbe632ba 100644
--- a/clang/lib/Basic/Targets/X86.cpp
+++ b/clang/lib/Basic/Targets/X86.cpp
@@ -220,6 +220,7 @@ bool X86TargetInfo::initFeatureMap(
     LLVM_FALLTHROUGH;
   case CK_Core2:
     setFeatureEnabledImpl(Features, "ssse3", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     LLVM_FALLTHROUGH;
   case CK_Yonah:
   case CK_Prescott:
@@ -261,6 +262,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "ssse3", true);
     setFeatureEnabledImpl(Features, "fxsr", true);
     setFeatureEnabledImpl(Features, "cx16", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     break;
 
   case CK_KNM:
@@ -291,6 +293,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "xsaveopt", true);
     setFeatureEnabledImpl(Features, "xsave", true);
     setFeatureEnabledImpl(Features, "movbe", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     break;
 
   case CK_K6_2:
@@ -304,6 +307,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "sse4a", true);
     setFeatureEnabledImpl(Features, "lzcnt", true);
     setFeatureEnabledImpl(Features, "popcnt", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     LLVM_FALLTHROUGH;
   case CK_K8SSE3:
     setFeatureEnabledImpl(Features, "sse3", true);
@@ -337,6 +341,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "prfchw", true);
     setFeatureEnabledImpl(Features, "cx16", true);
     setFeatureEnabledImpl(Features, "fxsr", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     break;
 
   case CK_ZNVER1:
@@ -360,6 +365,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "prfchw", true);
     setFeatureEnabledImpl(Features, "rdrnd", true);
     setFeatureEnabledImpl(Features, "rdseed", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     setFeatureEnabledImpl(Features, "sha", true);
     setFeatureEnabledImpl(Features, "sse4a", true);
     setFeatureEnabledImpl(Features, "xsave", true);
@@ -394,6 +400,7 @@ bool X86TargetInfo::initFeatureMap(
     setFeatureEnabledImpl(Features, "cx16", true);
     setFeatureEnabledImpl(Features, "fxsr", true);
     setFeatureEnabledImpl(Features, "xsave", true);
+    setFeatureEnabledImpl(Features, "sahf", true);
     break;
   }
   if (!TargetInfo::initFeatureMap(Features, Diags, CPU, FeaturesVec))
@@ -792,6 +799,8 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasRetpoline = true;
     } else if (Feature == "+retpoline-external-thunk") {
       HasRetpolineExternalThunk = true;
+    } else if (Feature == "+sahf") {
+      HasLAHFSAHF = true;
     }
 
     X86SSEEnum Level = llvm::StringSwitch<X86SSEEnum>(Feature)
@@ -1269,6 +1278,7 @@ bool X86TargetInfo::isValidFeatureName(StringRef Name) const {
       .Case("rdrnd", true)
       .Case("rdseed", true)
       .Case("rtm", true)
+      .Case("sahf", true)
       .Case("sgx", true)
       .Case("sha", true)
       .Case("shstk", true)
@@ -1343,6 +1353,7 @@ bool X86TargetInfo::hasFeature(StringRef Feature) const {
       .Case("retpoline", HasRetpoline)
       .Case("retpoline-external-thunk", HasRetpolineExternalThunk)
       .Case("rtm", HasRTM)
+      .Case("sahf", HasLAHFSAHF)
       .Case("sgx", HasSGX)
       .Case("sha", HasSHA)
       .Case("shstk", HasSHSTK)
diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index b46778f3da8..660e5847d68 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -99,6 +99,7 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
   bool HasRDPID = false;
   bool HasRetpoline = false;
   bool HasRetpolineExternalThunk = false;
+  bool HasLAHFSAHF = false;
 
 protected:
   /// \brief Enumeration of all of the X86 CPUs supported by Clang.