Auto merge of #55698 - nikic:remove-llvm-4-support, r=alexcrichton

Remove support for building against LLVM 4

With emscripten removed in #55626, we no longer need to support building against LLVM 4.

6 files changed, 29 insertions, 259 deletions

diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index 76faffa2521..60b06c579cb 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -595,9 +595,7 @@ fn run_pass_manager(cgcx: &CodegenContext,
         };
         with_llvm_pmb(llmod, config, opt_level, false, &mut |b| {
             if thin {
-                if !llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm) {
-                    panic!("this version of LLVM does not support ThinLTO");
-                }
+                llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm);
             } else {
                 llvm::LLVMPassManagerBuilderPopulateLTOPassManager(b, pm,
                     /* Internalize = */ False,
diff --git a/src/librustc_codegen_llvm/builder.rs b/src/librustc_codegen_llvm/builder.rs
index 1b1a31def37..9db4015013e 100644
--- a/src/librustc_codegen_llvm/builder.rs
+++ b/src/librustc_codegen_llvm/builder.rs
@@ -874,8 +874,7 @@ impl Builder<'a, 'll, 'tcx> {
             // FIXME: add a non-fast math version once
             // https://bugs.llvm.org/show_bug.cgi?id=36732
             // is fixed.
-            let instr = llvm::LLVMRustBuildVectorReduceFAdd(self.llbuilder, acc, src)
-                .expect("LLVMRustBuildVectorReduceFAdd is not available in LLVM version < 5.0");
+            let instr = llvm::LLVMRustBuildVectorReduceFAdd(self.llbuilder, acc, src);
             llvm::LLVMRustSetHasUnsafeAlgebra(instr);
             instr
         }
@@ -886,66 +885,43 @@ impl Builder<'a, 'll, 'tcx> {
             // FIXME: add a non-fast math version once
             // https://bugs.llvm.org/show_bug.cgi?id=36732
             // is fixed.
-            let instr = llvm::LLVMRustBuildVectorReduceFMul(self.llbuilder, acc, src)
-                .expect("LLVMRustBuildVectorReduceFMul is not available in LLVM version < 5.0");
+            let instr = llvm::LLVMRustBuildVectorReduceFMul(self.llbuilder, acc, src);
             llvm::LLVMRustSetHasUnsafeAlgebra(instr);
             instr
         }
     }
     pub fn vector_reduce_add(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.add");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceAdd(self.llbuilder, src);
-            instr.expect("LLVMRustBuildVectorReduceAdd is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceAdd(self.llbuilder, src) }
     }
     pub fn vector_reduce_mul(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.mul");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceMul(self.llbuilder, src);
-            instr.expect("LLVMRustBuildVectorReduceMul is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceMul(self.llbuilder, src) }
     }
     pub fn vector_reduce_and(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.and");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceAnd(self.llbuilder, src);
-            instr.expect("LLVMRustBuildVectorReduceAnd is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceAnd(self.llbuilder, src) }
     }
     pub fn vector_reduce_or(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.or");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceOr(self.llbuilder, src);
-            instr.expect("LLVMRustBuildVectorReduceOr is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceOr(self.llbuilder, src) }
     }
     pub fn vector_reduce_xor(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.xor");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceXor(self.llbuilder, src);
-            instr.expect("LLVMRustBuildVectorReduceXor is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceXor(self.llbuilder, src) }
     }
     pub fn vector_reduce_fmin(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.fmin");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceFMin(self.llbuilder, src, /*NoNaNs:*/ false);
-            instr.expect("LLVMRustBuildVectorReduceFMin is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceFMin(self.llbuilder, src, /*NoNaNs:*/ false) }
     }
     pub fn vector_reduce_fmax(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.fmax");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceFMax(self.llbuilder, src, /*NoNaNs:*/ false);
-            instr.expect("LLVMRustBuildVectorReduceFMax is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceFMax(self.llbuilder, src, /*NoNaNs:*/ false) }
     }
     pub fn vector_reduce_fmin_fast(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.fmin_fast");
         unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceFMin(self.llbuilder, src, /*NoNaNs:*/ true)
-                .expect("LLVMRustBuildVectorReduceFMin is not available in LLVM version < 5.0");
+            let instr = llvm::LLVMRustBuildVectorReduceFMin(self.llbuilder, src, /*NoNaNs:*/ true);
             llvm::LLVMRustSetHasUnsafeAlgebra(instr);
             instr
         }
@@ -953,25 +929,18 @@ impl Builder<'a, 'll, 'tcx> {
     pub fn vector_reduce_fmax_fast(&self, src: &'ll Value) -> &'ll Value {
         self.count_insn("vector.reduce.fmax_fast");
         unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceFMax(self.llbuilder, src, /*NoNaNs:*/ true)
-                .expect("LLVMRustBuildVectorReduceFMax is not available in LLVM version < 5.0");
+            let instr = llvm::LLVMRustBuildVectorReduceFMax(self.llbuilder, src, /*NoNaNs:*/ true);
             llvm::LLVMRustSetHasUnsafeAlgebra(instr);
             instr
         }
     }
     pub fn vector_reduce_min(&self, src: &'ll Value, is_signed: bool) -> &'ll Value {
         self.count_insn("vector.reduce.min");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceMin(self.llbuilder, src, is_signed);
-            instr.expect("LLVMRustBuildVectorReduceMin is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceMin(self.llbuilder, src, is_signed) }
     }
     pub fn vector_reduce_max(&self, src: &'ll Value, is_signed: bool) -> &'ll Value {
         self.count_insn("vector.reduce.max");
-        unsafe {
-            let instr = llvm::LLVMRustBuildVectorReduceMax(self.llbuilder, src, is_signed);
-            instr.expect("LLVMRustBuildVectorReduceMax is not available in LLVM version < 5.0")
-        }
+        unsafe { llvm::LLVMRustBuildVectorReduceMax(self.llbuilder, src, is_signed) }
     }
 
     pub fn extract_value(&self, agg_val: &'ll Value, idx: u64) -> &'ll Value {
diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index b994b1ffc4b..612581c1ac6 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -1057,42 +1057,42 @@ extern "C" {
     pub fn LLVMRustBuildVectorReduceFAdd(B: &Builder<'a>,
                                          Acc: &'a Value,
                                          Src: &'a Value)
-                                         -> Option<&'a Value>;
+                                         -> &'a Value;
     pub fn LLVMRustBuildVectorReduceFMul(B: &Builder<'a>,
                                          Acc: &'a Value,
                                          Src: &'a Value)
-                                         -> Option<&'a Value>;
+                                         -> &'a Value;
     pub fn LLVMRustBuildVectorReduceAdd(B: &Builder<'a>,
                                         Src: &'a Value)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceMul(B: &Builder<'a>,
                                         Src: &'a Value)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceAnd(B: &Builder<'a>,
                                         Src: &'a Value)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceOr(B: &Builder<'a>,
                                        Src: &'a Value)
-                                       -> Option<&'a Value>;
+                                       -> &'a Value;
     pub fn LLVMRustBuildVectorReduceXor(B: &Builder<'a>,
                                         Src: &'a Value)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceMin(B: &Builder<'a>,
                                         Src: &'a Value,
                                         IsSigned: bool)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceMax(B: &Builder<'a>,
                                         Src: &'a Value,
                                         IsSigned: bool)
-                                        -> Option<&'a Value>;
+                                        -> &'a Value;
     pub fn LLVMRustBuildVectorReduceFMin(B: &Builder<'a>,
                                          Src: &'a Value,
                                          IsNaN: bool)
-                                         -> Option<&'a Value>;
+                                         -> &'a Value;
     pub fn LLVMRustBuildVectorReduceFMax(B: &Builder<'a>,
                                          Src: &'a Value,
                                          IsNaN: bool)
-                                         -> Option<&'a Value>;
+                                         -> &'a Value;
 
     pub fn LLVMRustBuildMinNum(
         B: &Builder<'a>,
@@ -1173,7 +1173,7 @@ extern "C" {
                                                         RunInliner: Bool);
     pub fn LLVMRustPassManagerBuilderPopulateThinLTOPassManager(
         PMB: &PassManagerBuilder,
-        PM: &PassManager) -> bool;
+        PM: &PassManager);
 
     // Stuff that's in rustllvm/ because it's not upstream yet.
 
diff --git a/src/rustllvm/ArchiveWrapper.cpp b/src/rustllvm/ArchiveWrapper.cpp
index 390450a5205..1355c0377ce 100644
--- a/src/rustllvm/ArchiveWrapper.cpp
+++ b/src/rustllvm/ArchiveWrapper.cpp
@@ -204,9 +204,7 @@ LLVMRustWriteArchive(char *Dst, size_t NumMembers,
         LLVMRustSetLastError(toString(MOrErr.takeError()).c_str());
         return LLVMRustResult::Failure;
       }
-#if LLVM_VERSION_GE(5, 0)
       MOrErr->MemberName = sys::path::filename(MOrErr->MemberName);
-#endif
       Members.push_back(std::move(*MOrErr));
     } else {
       Expected<NewArchiveMember> MOrErr =
diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index e8bfa222207..3b0046222a9 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -36,9 +36,6 @@
 #include "llvm/Transforms/IPO/FunctionImport.h"
 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
 #include "llvm/LTO/LTO.h"
-#if LLVM_VERSION_LE(4, 0)
-#include "llvm/Object/ModuleSummaryIndexObjectFile.h"
-#endif
 
 #include "llvm-c/Transforms/PassManagerBuilder.h"
 
@@ -111,12 +108,11 @@ extern "C" void LLVMRustAddPass(LLVMPassManagerRef PMR, LLVMPassRef RustPass) {
 }
 
 extern "C"
-bool LLVMRustPassManagerBuilderPopulateThinLTOPassManager(
+void LLVMRustPassManagerBuilderPopulateThinLTOPassManager(
   LLVMPassManagerBuilderRef PMBR,
   LLVMPassManagerRef PMR
 ) {
   unwrap(PMBR)->populateThinLTOPassManager(*unwrap(PMR));
-  return true;
 }
 
 #ifdef LLVM_COMPONENT_X86
@@ -869,21 +865,10 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
 
     Ret->ModuleMap[module->identifier] = mem_buffer;
 
-#if LLVM_VERSION_GE(5, 0)
     if (Error Err = readModuleSummaryIndex(mem_buffer, Ret->Index, i)) {
       LLVMRustSetLastError(toString(std::move(Err)).c_str());
       return nullptr;
     }
-#else
-    Expected<std::unique_ptr<object::ModuleSummaryIndexObjectFile>> ObjOrErr =
-      object::ModuleSummaryIndexObjectFile::create(mem_buffer);
-    if (!ObjOrErr) {
-      LLVMRustSetLastError(toString(ObjOrErr.takeError()).c_str());
-      return nullptr;
-    }
-    auto Index = (*ObjOrErr)->takeIndex();
-    Ret->Index.mergeFrom(std::move(Index), i);
-#endif
   }
 
   // Collect for each module the list of function it defines (GUID -> Summary)
@@ -900,7 +885,6 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
   // combined index
   //
   // This is copied from `lib/LTO/ThinLTOCodeGenerator.cpp`
-#if LLVM_VERSION_GE(5, 0)
 #if LLVM_VERSION_GE(7, 0)
   auto deadIsPrevailing = [&](GlobalValue::GUID G) {
     return PrevailingType::Unknown;
@@ -915,16 +899,6 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
     Ret->ImportLists,
     Ret->ExportLists
   );
-#else
-  auto DeadSymbols = computeDeadSymbols(Ret->Index, Ret->GUIDPreservedSymbols);
-  ComputeCrossModuleImport(
-    Ret->Index,
-    Ret->ModuleToDefinedGVSummaries,
-    Ret->ImportLists,
-    Ret->ExportLists,
-    &DeadSymbols
-  );
-#endif
 
   // Resolve LinkOnce/Weak symbols, this has to be computed early be cause it
   // impacts the caching.
@@ -934,13 +908,8 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
   DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
   for (auto &I : Ret->Index) {
-#if LLVM_VERSION_GE(5, 0)
     if (I.second.SummaryList.size() > 1)
       PrevailingCopy[I.first] = getFirstDefinitionForLinker(I.second.SummaryList);
-#else
-    if (I.second.size() > 1)
-      PrevailingCopy[I.first] = getFirstDefinitionForLinker(I.second);
-#endif
   }
   auto isPrevailing = [&](GlobalValue::GUID GUID, const GlobalValueSummary *S) {
     const auto &Prevailing = PrevailingCopy.find(GUID);
@@ -962,19 +931,11 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
   // linkage will stay as external, and internal will stay as internal.
   std::set<GlobalValue::GUID> ExportedGUIDs;
   for (auto &List : Ret->Index) {
-#if LLVM_VERSION_GE(5, 0)
     for (auto &GVS: List.second.SummaryList) {
-#else
-    for (auto &GVS: List.second) {
-#endif
       if (GlobalValue::isLocalLinkage(GVS->linkage()))
         continue;
       auto GUID = GVS->getOriginalName();
-#if LLVM_VERSION_GE(5, 0)
       if (GVS->flags().Live)
-#else
-      if (!DeadSymbols.count(GUID))
-#endif
         ExportedGUIDs.insert(GUID);
     }
   }
diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index f00b7f3a58f..f423503e19f 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #include "rustllvm.h"
+#include "llvm/IR/CallSite.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/DiagnosticPrinter.h"
@@ -18,14 +19,7 @@
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm/Support/Signals.h"
-
-#include "llvm/IR/CallSite.h"
-
-#if LLVM_VERSION_GE(5, 0)
 #include "llvm/ADT/Optional.h"
-#else
-#include <cstdlib>
-#endif
 
 #include <iostream>
 
@@ -212,14 +206,7 @@ extern "C" void LLVMRustAddCallSiteAttribute(LLVMValueRef Instr, unsigned Index,
                                              LLVMRustAttribute RustAttr) {
   CallSite Call = CallSite(unwrap<Instruction>(Instr));
   Attribute Attr = Attribute::get(Call->getContext(), fromRust(RustAttr));
-#if LLVM_VERSION_GE(5, 0)
   Call.addAttribute(Index, Attr);
-#else
-  AttrBuilder B(Attr);
-  Call.setAttributes(Call.getAttributes().addAttributes(
-      Call->getContext(), Index,
-      AttributeSet::get(Call->getContext(), Index, B)));
-#endif
 }
 
 extern "C" void LLVMRustAddAlignmentCallSiteAttr(LLVMValueRef Instr,
@@ -228,14 +215,8 @@ extern "C" void LLVMRustAddAlignmentCallSiteAttr(LLVMValueRef Instr,
   CallSite Call = CallSite(unwrap<Instruction>(Instr));
   AttrBuilder B;
   B.addAlignmentAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   Call.setAttributes(Call.getAttributes().addAttributes(
       Call->getContext(), Index, B));
-#else
-  Call.setAttributes(Call.getAttributes().addAttributes(
-      Call->getContext(), Index,
-      AttributeSet::get(Call->getContext(), Index, B)));
-#endif
 }
 
 extern "C" void LLVMRustAddDereferenceableCallSiteAttr(LLVMValueRef Instr,
@@ -244,14 +225,8 @@ extern "C" void LLVMRustAddDereferenceableCallSiteAttr(LLVMValueRef Instr,
   CallSite Call = CallSite(unwrap<Instruction>(Instr));
   AttrBuilder B;
   B.addDereferenceableAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   Call.setAttributes(Call.getAttributes().addAttributes(
       Call->getContext(), Index, B));
-#else
-  Call.setAttributes(Call.getAttributes().addAttributes(
-      Call->getContext(), Index,
-      AttributeSet::get(Call->getContext(), Index, B)));
-#endif
 }
 
 extern "C" void LLVMRustAddDereferenceableOrNullCallSiteAttr(LLVMValueRef Instr,
@@ -260,14 +235,8 @@ extern "C" void LLVMRustAddDereferenceableOrNullCallSiteAttr(LLVMValueRef Instr,
   CallSite Call = CallSite(unwrap<Instruction>(Instr));
   AttrBuilder B;
   B.addDereferenceableOrNullAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   Call.setAttributes(Call.getAttributes().addAttributes(
       Call->getContext(), Index, B));
-#else
-  Call.setAttributes(Call.getAttributes().addAttributes(
-      Call->getContext(), Index,
-      AttributeSet::get(Call->getContext(), Index, B)));
-#endif
 }
 
 extern "C" void LLVMRustAddFunctionAttribute(LLVMValueRef Fn, unsigned Index,
@@ -275,11 +244,7 @@ extern "C" void LLVMRustAddFunctionAttribute(LLVMValueRef Fn, unsigned Index,
   Function *A = unwrap<Function>(Fn);
   Attribute Attr = Attribute::get(A->getContext(), fromRust(RustAttr));
   AttrBuilder B(Attr);
-#if LLVM_VERSION_GE(5, 0)
   A->addAttributes(Index, B);
-#else
-  A->addAttributes(Index, AttributeSet::get(A->getContext(), Index, B));
-#endif
 }
 
 extern "C" void LLVMRustAddAlignmentAttr(LLVMValueRef Fn,
@@ -288,11 +253,7 @@ extern "C" void LLVMRustAddAlignmentAttr(LLVMValueRef Fn,
   Function *A = unwrap<Function>(Fn);
   AttrBuilder B;
   B.addAlignmentAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   A->addAttributes(Index, B);
-#else
-  A->addAttributes(Index, AttributeSet::get(A->getContext(), Index, B));
-#endif
 }
 
 extern "C" void LLVMRustAddDereferenceableAttr(LLVMValueRef Fn, unsigned Index,
@@ -300,11 +261,7 @@ extern "C" void LLVMRustAddDereferenceableAttr(LLVMValueRef Fn, unsigned Index,
   Function *A = unwrap<Function>(Fn);
   AttrBuilder B;
   B.addDereferenceableAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   A->addAttributes(Index, B);
-#else
-  A->addAttributes(Index, AttributeSet::get(A->getContext(), Index, B));
-#endif
 }
 
 extern "C" void LLVMRustAddDereferenceableOrNullAttr(LLVMValueRef Fn,
@@ -313,11 +270,7 @@ extern "C" void LLVMRustAddDereferenceableOrNullAttr(LLVMValueRef Fn,
   Function *A = unwrap<Function>(Fn);
   AttrBuilder B;
   B.addDereferenceableOrNullAttr(Bytes);
-#if LLVM_VERSION_GE(5, 0)
   A->addAttributes(Index, B);
-#else
-  A->addAttributes(Index, AttributeSet::get(A->getContext(), Index, B));
-#endif
 }
 
 extern "C" void LLVMRustAddFunctionAttrStringValue(LLVMValueRef Fn,
@@ -327,11 +280,7 @@ extern "C" void LLVMRustAddFunctionAttrStringValue(LLVMValueRef Fn,
   Function *F = unwrap<Function>(Fn);
   AttrBuilder B;
   B.addAttribute(Name, Value);
-#if LLVM_VERSION_GE(5, 0)
   F->addAttributes(Index, B);
-#else
-  F->addAttributes(Index, AttributeSet::get(F->getContext(), Index, B));
-#endif
 }
 
 extern "C" void LLVMRustRemoveFunctionAttributes(LLVMValueRef Fn,
@@ -341,12 +290,7 @@ extern "C" void LLVMRustRemoveFunctionAttributes(LLVMValueRef Fn,
   Attribute Attr = Attribute::get(F->getContext(), fromRust(RustAttr));
   AttrBuilder B(Attr);
   auto PAL = F->getAttributes();
-#if LLVM_VERSION_GE(5, 0)
   auto PALNew = PAL.removeAttributes(F->getContext(), Index, B);
-#else
-  const AttributeSet PALNew = PAL.removeAttributes(
-      F->getContext(), Index, AttributeSet::get(F->getContext(), Index, B));
-#endif
   F->setAttributes(PALNew);
 }
 
@@ -396,7 +340,6 @@ enum class LLVMRustSynchronizationScope {
   CrossThread,
 };
 
-#if LLVM_VERSION_GE(5, 0)
 static SyncScope::ID fromRust(LLVMRustSynchronizationScope Scope) {
   switch (Scope) {
   case LLVMRustSynchronizationScope::SingleThread:
@@ -407,18 +350,6 @@ static SyncScope::ID fromRust(LLVMRustSynchronizationScope Scope) {
     report_fatal_error("bad SynchronizationScope.");
   }
 }
-#else
-static SynchronizationScope fromRust(LLVMRustSynchronizationScope Scope) {
-  switch (Scope) {
-  case LLVMRustSynchronizationScope::SingleThread:
-    return SingleThread;
-  case LLVMRustSynchronizationScope::CrossThread:
-    return CrossThread;
-  default:
-    report_fatal_error("bad SynchronizationScope.");
-  }
-}
-#endif
 
 extern "C" LLVMValueRef
 LLVMRustBuildAtomicFence(LLVMBuilderRef B, LLVMAtomicOrdering Order,
@@ -463,18 +394,6 @@ extern "C" void LLVMRustAppendModuleInlineAsm(LLVMModuleRef M, const char *Asm)
 
 typedef DIBuilder *LLVMRustDIBuilderRef;
 
-#if LLVM_VERSION_LT(5, 0)
-typedef struct LLVMOpaqueMetadata *LLVMMetadataRef;
-
-namespace llvm {
-DEFINE_ISA_CONVERSION_FUNCTIONS(Metadata, LLVMMetadataRef)
-
-inline Metadata **unwrap(LLVMMetadataRef *Vals) {
-  return reinterpret_cast<Metadata **>(Vals);
-}
-}
-#endif
-
 template <typename DIT> DIT *unwrapDIPtr(LLVMMetadataRef Ref) {
   return (DIT *)(Ref ? unwrap<MDNode>(Ref) : nullptr);
 }
@@ -590,11 +509,6 @@ static DINode::DIFlags fromRust(LLVMRustDIFlags Flags) {
   if (isSet(Flags & LLVMRustDIFlags::FlagRValueReference)) {
     Result |= DINode::DIFlags::FlagRValueReference;
   }
-#if LLVM_VERSION_LE(4, 0)
-  if (isSet(Flags & LLVMRustDIFlags::FlagExternalTypeRef)) {
-    Result |= DINode::DIFlags::FlagExternalTypeRef;
-  }
-#endif
   if (isSet(Flags & LLVMRustDIFlags::FlagIntroducedVirtual)) {
     Result |= DINode::DIFlags::FlagIntroducedVirtual;
   }
@@ -693,9 +607,7 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreatePointerType(
     uint64_t SizeInBits, uint32_t AlignInBits, const char *Name) {
   return wrap(Builder->createPointerType(unwrapDI<DIType>(PointeeTy),
                                          SizeInBits, AlignInBits,
-#if LLVM_VERSION_GE(5, 0)
                                          /* DWARFAddressSpace */ None,
-#endif
                                          Name));
 }
 
@@ -902,12 +814,7 @@ LLVMRustDIBuilderCreateNameSpace(LLVMRustDIBuilderRef Builder,
                                  LLVMMetadataRef Scope, const char *Name,
                                  LLVMMetadataRef File, unsigned LineNo) {
   return wrap(Builder->createNameSpace(
-      unwrapDI<DIDescriptor>(Scope), Name
-#if LLVM_VERSION_LT(5, 0)
-      ,
-      unwrapDI<DIFile>(File), LineNo
-#endif
-      ,
+      unwrapDI<DIDescriptor>(Scope), Name,
       false // ExportSymbols (only relevant for C++ anonymous namespaces)
       ));
 }
@@ -937,12 +844,7 @@ extern "C" int64_t LLVMRustDIBuilderCreateOpDeref() {
 }
 
 extern "C" int64_t LLVMRustDIBuilderCreateOpPlusUconst() {
-#if LLVM_VERSION_GE(5, 0)
   return dwarf::DW_OP_plus_uconst;
-#else
-  // older LLVM used `plus` to behave like `plus_uconst`.
-  return dwarf::DW_OP_plus;
-#endif
 }
 
 extern "C" void LLVMRustWriteTypeToString(LLVMTypeRef Ty, RustStringRef Str) {
@@ -1014,21 +916,12 @@ extern "C" void LLVMRustUnpackOptimizationDiagnostic(
   *FunctionOut = wrap(&Opt->getFunction());
 
   RawRustStringOstream FilenameOS(FilenameOut);
-#if LLVM_VERSION_GE(5,0)
   DiagnosticLocation loc = Opt->getLocation();
   if (loc.isValid()) {
     *Line = loc.getLine();
     *Column = loc.getColumn();
     FilenameOS << loc.getFilename();
   }
-#else
-  const DebugLoc &loc = Opt->getDebugLoc();
-  if (loc) {
-    *Line = loc.getLine();
-    *Column = loc.getCol();
-    FilenameOS << cast<DIScope>(loc.getScope())->getFilename();
-  }
-#endif
 
   RawRustStringOstream MessageOS(MessageOut);
   MessageOS << Opt->getMsg();
@@ -1485,7 +1378,6 @@ LLVMRustModuleCost(LLVMModuleRef M) {
 }
 
 // Vector reductions:
-#if LLVM_VERSION_GE(5, 0)
 extern "C" LLVMValueRef
 LLVMRustBuildVectorReduceFAdd(LLVMBuilderRef B, LLVMValueRef Acc, LLVMValueRef Src) {
     return wrap(unwrap(B)->CreateFAddReduce(unwrap(Acc),unwrap(Src)));
@@ -1531,54 +1423,6 @@ LLVMRustBuildVectorReduceFMax(LLVMBuilderRef B, LLVMValueRef Src, bool NoNaN) {
   return wrap(unwrap(B)->CreateFPMaxReduce(unwrap(Src), NoNaN));
 }
 
-#else
-
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceFAdd(LLVMBuilderRef, LLVMValueRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceFMul(LLVMBuilderRef, LLVMValueRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceAdd(LLVMBuilderRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceMul(LLVMBuilderRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceAnd(LLVMBuilderRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceOr(LLVMBuilderRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceXor(LLVMBuilderRef, LLVMValueRef) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceMin(LLVMBuilderRef, LLVMValueRef, bool) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceMax(LLVMBuilderRef, LLVMValueRef, bool) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceFMin(LLVMBuilderRef, LLVMValueRef, bool) {
-  return nullptr;
-}
-extern "C" LLVMValueRef
-LLVMRustBuildVectorReduceFMax(LLVMBuilderRef, LLVMValueRef, bool) {
-  return nullptr;
-}
-#endif
-
 #if LLVM_VERSION_GE(6, 0)
 extern "C" LLVMValueRef
 LLVMRustBuildMinNum(LLVMBuilderRef B, LLVMValueRef LHS, LLVMValueRef RHS) {