Implement feature extraction from `TargetMachine`

Add the `LLVMRustHasFeature` function to check whether a
`TargetMachine` has a given feature.

mk/rustllvm.mk

@@ -43,6 +43,9 @@ $$(RT_OUTPUT_DIR_$(1))/$$(call CFG_STATIC_LIB_NAME_$(1),rustllvm): \
 	@$$(call E, link: $$@)
 	$$(Q)$$(call CFG_CREATE_ARCHIVE_$(1),$$@) $$^
 
+RUSTLLVM_COMPONENTS_$(1) = $$(shell echo $$(LLVM_ALL_COMPONENTS_$(1)) |\
+	tr 'a-z-' 'A-Z_'| sed -e 's/^ //;s/\([^ ]*\)/\-DLLVM_COMPONENT_\1/g')
+
 # On MSVC we need to double-escape arguments that llvm-config printed which
 # start with a '/'. The shell we're running in will auto-translate the argument
 # `/foo` to `C:/msys64/foo` but we really want it to be passed through as `/foo`
@@ -51,6 +54,7 @@ $(1)/rustllvm/%.o: $(S)src/rustllvm/%.cpp $$(MKFILE_DEPS) $$(LLVM_CONFIG_$(1))
 	@$$(call E, compile: $$@)
 	$$(Q)$$(call CFG_COMPILE_CXX_$(1), $$@,) \
 		$$(subst  /,//,$$(LLVM_CXXFLAGS_$(1))) \
+		$$(RUSTLLVM_COMPONENTS_$(1)) \
 		$$(EXTRA_RUSTLLVM_CXXFLAGS_$(1)) \
 		$$(RUSTLLVM_INCS_$(1)) \
 		$$<

src/librustc_llvm/build.rs

@@ -100,6 +100,13 @@ fn main() {
         }
         cfg.flag(flag);
     }
+
+    for component in &components[..] {
+        let mut flag = String::from("-DLLVM_COMPONENT_");
+        flag.push_str(&component.to_uppercase());
+        cfg.flag(&flag);
+    }
+
     cfg.file("../rustllvm/ExecutionEngineWrapper.cpp")
        .file("../rustllvm/PassWrapper.cpp")
        .file("../rustllvm/RustWrapper.cpp")

src/librustc_llvm/lib.rs

@@ -2013,6 +2013,9 @@ extern {
     pub fn LLVMRustFindAndCreatePass(Pass: *const c_char) -> PassRef;
     pub fn LLVMRustAddPass(PM: PassManagerRef, Pass: PassRef);
 
+    pub fn LLVMRustHasFeature(T: TargetMachineRef,
+                              s: *const c_char) -> bool;
+
     pub fn LLVMRustCreateTargetMachine(Triple: *const c_char,
                                        CPU: *const c_char,
                                        Features: *const c_char,

src/rustllvm/PassWrapper.cpp

@@ -97,6 +97,75 @@ LLVMRustAddPass(LLVMPassManagerRef PM, Pass *pass) {
     pm->add(pass);
 }
 
+#ifdef LLVM_COMPONENT_X86
+#define SUBTARGET_X86 SUBTARGET(X86)
+#else
+#define SUBTARGET_X86
+#endif
+
+#ifdef LLVM_COMPONENT_ARM
+#define SUBTARGET_ARM SUBTARGET(ARM)
+#else
+#define SUBTARGET_ARM
+#endif
+
+#ifdef LLVM_COMPONENT_AARCH64
+#define SUBTARGET_AARCH64 SUBTARGET(AArch64)
+#else
+#define SUBTARGET_AARCH64
+#endif
+
+#ifdef LLVM_COMPONENT_MIPS
+#define SUBTARGET_MIPS SUBTARGET(Mips)
+#else
+#define SUBTARGET_MIPS
+#endif
+
+#ifdef LLVM_COMPONENT_POWERPC
+#define SUBTARGET_PPC SUBTARGET(PPC)
+#else
+#define SUBTARGET_PPC
+#endif
+
+#define GEN_SUBTARGETS    \
+        SUBTARGET_X86     \
+        SUBTARGET_ARM     \
+        SUBTARGET_AARCH64 \
+        SUBTARGET_MIPS    \
+        SUBTARGET_PPC
+
+#define SUBTARGET(x) namespace llvm {                \
+    extern const SubtargetFeatureKV x##FeatureKV[];  \
+    extern const SubtargetFeatureKV x##SubTypeKV[];  \
+  }
+
+GEN_SUBTARGETS
+#undef SUBTARGET
+
+extern "C" bool
+LLVMRustHasFeature(LLVMTargetMachineRef TM,
+		   const char *feature) {
+    TargetMachine *Target = unwrap(TM);
+    const MCSubtargetInfo *MCInfo = Target->getMCSubtargetInfo();
+    const FeatureBitset &Bits = MCInfo->getFeatureBits();
+    const llvm::SubtargetFeatureKV *FeatureEntry;
+
+#define SUBTARGET(x)                                        \
+    if (MCInfo->isCPUStringValid(x##SubTypeKV[0].Key)) {    \
+        FeatureEntry = x##FeatureKV;                       \
+    } else
+
+    GEN_SUBTARGETS {
+        return false;
+    }
+#undef SUBTARGET
+
+    while (strcmp(feature, FeatureEntry->Key) != 0)
+        FeatureEntry++;
+
+    return (Bits & FeatureEntry->Value) == FeatureEntry->Value;
+}
+
 extern "C" LLVMTargetMachineRef
 LLVMRustCreateTargetMachine(const char *triple,
                             const char *cpu,