Update the minimum external LLVM to 20

6 files changed, 66 insertions, 237 deletions

diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 7d0691366e6..0f17cc9063a 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1091,16 +1091,11 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         ty: Ty<'tcx>,
         lhs: Self::Value,
         rhs: Self::Value,
-    ) -> Option<Self::Value> {
-        // FIXME: See comment on the definition of `three_way_compare`.
-        if crate::llvm_util::get_version() < (20, 0, 0) {
-            return None;
-        }
-
+    ) -> Self::Value {
         let size = ty.primitive_size(self.tcx);
         let name = if ty.is_signed() { "llvm.scmp" } else { "llvm.ucmp" };
 
-        Some(self.call_intrinsic(name, &[self.type_i8(), self.type_ix(size.bits())], &[lhs, rhs]))
+        self.call_intrinsic(name, &[self.type_i8(), self.type_ix(size.bits())], &[lhs, rhs])
     }
 
     /* Miscellaneous instructions */
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index a69fa54a54a..5f4385c9c6a 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -172,35 +172,6 @@ pub(crate) unsafe fn create_module<'ll>(
     let mut target_data_layout = sess.target.data_layout.to_string();
     let llvm_version = llvm_util::get_version();
 
-    if llvm_version < (20, 0, 0) {
-        if sess.target.arch == "aarch64" || sess.target.arch.starts_with("arm64") {
-            // LLVM 20 defines three additional address spaces for alternate
-            // pointer kinds used in Windows.
-            // See https://github.com/llvm/llvm-project/pull/111879
-            target_data_layout =
-                target_data_layout.replace("-p270:32:32-p271:32:32-p272:64:64", "");
-        }
-        if sess.target.arch.starts_with("sparc") {
-            // LLVM 20 updates the sparc layout to correctly align 128 bit integers to 128 bit.
-            // See https://github.com/llvm/llvm-project/pull/106951
-            target_data_layout = target_data_layout.replace("-i128:128", "");
-        }
-        if sess.target.arch.starts_with("mips64") {
-            // LLVM 20 updates the mips64 layout to correctly align 128 bit integers to 128 bit.
-            // See https://github.com/llvm/llvm-project/pull/112084
-            target_data_layout = target_data_layout.replace("-i128:128", "");
-        }
-        if sess.target.arch.starts_with("powerpc64") {
-            // LLVM 20 updates the powerpc64 layout to correctly align 128 bit integers to 128 bit.
-            // See https://github.com/llvm/llvm-project/pull/118004
-            target_data_layout = target_data_layout.replace("-i128:128", "");
-        }
-        if sess.target.arch.starts_with("wasm32") || sess.target.arch.starts_with("wasm64") {
-            // LLVM 20 updates the wasm(32|64) layout to correctly align 128 bit integers to 128 bit.
-            // See https://github.com/llvm/llvm-project/pull/119204
-            target_data_layout = target_data_layout.replace("-i128:128", "");
-        }
-    }
     if llvm_version < (21, 0, 0) {
         if sess.target.arch == "nvptx64" {
             // LLVM 21 updated the default layout on nvptx: https://github.com/llvm/llvm-project/pull/124961
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index d927ffd78c2..8461c8b03d5 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -246,9 +246,6 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         ("aarch64", "pmuv3") => Some(LLVMFeature::new("perfmon")),
         ("aarch64", "paca") => Some(LLVMFeature::new("pauth")),
         ("aarch64", "pacg") => Some(LLVMFeature::new("pauth")),
-        // Before LLVM 20 those two features were packaged together as b16b16
-        ("aarch64", "sve-b16b16") if get_version().0 < 20 => Some(LLVMFeature::new("b16b16")),
-        ("aarch64", "sme-b16b16") if get_version().0 < 20 => Some(LLVMFeature::new("b16b16")),
         ("aarch64", "flagm2") => Some(LLVMFeature::new("altnzcv")),
         // Rust ties fp and neon together.
         ("aarch64", "neon") => Some(LLVMFeature::with_dependencies(
@@ -262,57 +259,17 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         // Filter out features that are not supported by the current LLVM version
         ("aarch64", "fpmr") => None, // only existed in 18
         ("arm", "fp16") => Some(LLVMFeature::new("fullfp16")),
-        // NVPTX targets added in LLVM 20
-        ("nvptx64", "sm_100") if get_version().0 < 20 => None,
-        ("nvptx64", "sm_100a") if get_version().0 < 20 => None,
-        ("nvptx64", "sm_101") if get_version().0 < 20 => None,
-        ("nvptx64", "sm_101a") if get_version().0 < 20 => None,
-        ("nvptx64", "sm_120") if get_version().0 < 20 => None,
-        ("nvptx64", "sm_120a") if get_version().0 < 20 => None,
-        ("nvptx64", "ptx86") if get_version().0 < 20 => None,
-        ("nvptx64", "ptx87") if get_version().0 < 20 => None,
         // Filter out features that are not supported by the current LLVM version
-        ("loongarch64", "div32" | "lam-bh" | "lamcas" | "ld-seq-sa" | "scq")
-            if get_version().0 < 20 =>
-        {
-            None
-        }
         ("loongarch32" | "loongarch64", "32s") if get_version().0 < 21 => None,
-        // Filter out features that are not supported by the current LLVM version
-        ("riscv32" | "riscv64", "zacas" | "rva23u64" | "supm") if get_version().0 < 20 => None,
-        (
-            "s390x",
-            "message-security-assist-extension12"
-            | "concurrent-functions"
-            | "miscellaneous-extensions-4"
-            | "vector-enhancements-3"
-            | "vector-packed-decimal-enhancement-3",
-        ) if get_version().0 < 20 => None,
         // Enable the evex512 target feature if an avx512 target feature is enabled.
         ("x86", s) if s.starts_with("avx512") => Some(LLVMFeature::with_dependencies(
             s,
             smallvec![TargetFeatureFoldStrength::EnableOnly("evex512")],
         )),
-        // Support for `wide-arithmetic` will first land in LLVM 20 as part of
-        // llvm/llvm-project#111598
-        ("wasm32" | "wasm64", "wide-arithmetic") if get_version() < (20, 0, 0) => None,
         ("sparc", "leoncasa") => Some(LLVMFeature::new("hasleoncasa")),
-        // In LLVM 19, there is no `v8plus` feature and `v9` means "SPARC-V9 instruction available and SPARC-V8+ ABI used".
-        // https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp#L27-L28
-        // Before LLVM 19, there was no `v8plus` feature and `v9` means "SPARC-V9 instruction available".
-        // https://github.com/llvm/llvm-project/blob/llvmorg-18.1.0/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp#L26
-        ("sparc", "v8plus") if get_version().0 == 19 => Some(LLVMFeature::new("v9")),
         ("powerpc", "power8-crypto") => Some(LLVMFeature::new("crypto")),
-        // These new `amx` variants and `movrs` were introduced in LLVM20
-        ("x86", "amx-avx512" | "amx-fp8" | "amx-movrs" | "amx-tf32" | "amx-transpose")
-            if get_version().0 < 20 =>
-        {
-            None
-        }
-        ("x86", "movrs") if get_version().0 < 20 => None,
         ("x86", "avx10.1") => Some(LLVMFeature::new("avx10.1-512")),
-        ("x86", "avx10.2") if get_version().0 < 20 => None,
-        ("x86", "avx10.2") if get_version().0 >= 20 => Some(LLVMFeature::new("avx10.2-512")),
+        ("x86", "avx10.2") => Some(LLVMFeature::new("avx10.2-512")),
         ("x86", "apxf") => Some(LLVMFeature::with_dependencies(
             "egpr",
             smallvec![
@@ -716,17 +673,7 @@ pub(crate) fn global_llvm_features(
     };
 
     // Features implied by an implicit or explicit `--target`.
-    features.extend(
-        sess.target
-            .features
-            .split(',')
-            .filter(|v| !v.is_empty())
-            // Drop +v8plus feature introduced in LLVM 20.
-            // (Hard-coded target features do not go through `to_llvm_feature` since they already
-            // are LLVM feature names, hence we need a special case here.)
-            .filter(|v| *v != "+v8plus" || get_version() >= (20, 0, 0))
-            .map(String::from),
-    );
+    features.extend(sess.target.features.split(',').filter(|v| !v.is_empty()).map(String::from));
 
     if wants_wasm_eh(sess) && sess.panic_strategy() == PanicStrategy::Unwind {
         features.push("+exception-handling".into());
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index f8755874014..4c9bb7cf8a8 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -901,36 +901,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 }
             }
             mir::BinOp::Cmp => {
-                use std::cmp::Ordering;
                 assert!(!is_float);
-                if let Some(value) = bx.three_way_compare(lhs_ty, lhs, rhs) {
-                    return value;
-                }
-                let pred = |op| base::bin_op_to_icmp_predicate(op, is_signed);
-                if bx.cx().tcx().sess.opts.optimize == OptLevel::No {
-                    // FIXME: This actually generates tighter assembly, and is a classic trick
-                    // <https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>
-                    // However, as of 2023-11 it optimizes worse in things like derived
-                    // `PartialOrd`, so only use it in debug for now. Once LLVM can handle it
-                    // better (see <https://github.com/llvm/llvm-project/issues/73417>), it'll
-                    // be worth trying it in optimized builds as well.
-                    let is_gt = bx.icmp(pred(mir::BinOp::Gt), lhs, rhs);
-                    let gtext = bx.zext(is_gt, bx.type_i8());
-                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
-                    let ltext = bx.zext(is_lt, bx.type_i8());
-                    bx.unchecked_ssub(gtext, ltext)
-                } else {
-                    // These operations are those expected by `tests/codegen-llvm/integer-cmp.rs`,
-                    // from <https://github.com/rust-lang/rust/pull/63767>.
-                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
-                    let is_ne = bx.icmp(pred(mir::BinOp::Ne), lhs, rhs);
-                    let ge = bx.select(
-                        is_ne,
-                        bx.cx().const_i8(Ordering::Greater as i8),
-                        bx.cx().const_i8(Ordering::Equal as i8),
-                    );
-                    bx.select(is_lt, bx.cx().const_i8(Ordering::Less as i8), ge)
-                }
+                bx.three_way_compare(lhs_ty, lhs, rhs)
             }
             mir::BinOp::AddWithOverflow
             | mir::BinOp::SubWithOverflow
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index f417d1a7bf7..422fa715de1 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -3,6 +3,7 @@ use std::ops::Deref;
 
 use rustc_abi::{Align, Scalar, Size, WrappingRange};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
+use rustc_middle::mir;
 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{AtomicOrdering, Instance, Ty};
 use rustc_session::config::OptLevel;
@@ -405,15 +406,38 @@ pub trait BuilderMethods<'a, 'tcx>:
     fn fcmp(&mut self, op: RealPredicate, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
 
     /// Returns `-1` if `lhs < rhs`, `0` if `lhs == rhs`, and `1` if `lhs > rhs`.
-    // FIXME: Move the default implementation from `codegen_scalar_binop` into this method and
-    // remove the `Option` return once LLVM 20 is the minimum version.
     fn three_way_compare(
         &mut self,
-        _ty: Ty<'tcx>,
-        _lhs: Self::Value,
-        _rhs: Self::Value,
-    ) -> Option<Self::Value> {
-        None
+        ty: Ty<'tcx>,
+        lhs: Self::Value,
+        rhs: Self::Value,
+    ) -> Self::Value {
+        use std::cmp::Ordering;
+        let pred = |op| crate::base::bin_op_to_icmp_predicate(op, ty.is_signed());
+        if self.cx().sess().opts.optimize == OptLevel::No {
+            // FIXME: This actually generates tighter assembly, and is a classic trick
+            // <https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>
+            // However, as of 2023-11 it optimizes worse in things like derived
+            // `PartialOrd`, so only use it in debug for now. Once LLVM can handle it
+            // better (see <https://github.com/llvm/llvm-project/issues/73417>), it'll
+            // be worth trying it in optimized builds as well.
+            let is_gt = self.icmp(pred(mir::BinOp::Gt), lhs, rhs);
+            let gtext = self.zext(is_gt, self.type_i8());
+            let is_lt = self.icmp(pred(mir::BinOp::Lt), lhs, rhs);
+            let ltext = self.zext(is_lt, self.type_i8());
+            self.unchecked_ssub(gtext, ltext)
+        } else {
+            // These operations are those expected by `tests/codegen-llvm/integer-cmp.rs`,
+            // from <https://github.com/rust-lang/rust/pull/63767>.
+            let is_lt = self.icmp(pred(mir::BinOp::Lt), lhs, rhs);
+            let is_ne = self.icmp(pred(mir::BinOp::Ne), lhs, rhs);
+            let ge = self.select(
+                is_ne,
+                self.cx().const_i8(Ordering::Greater as i8),
+                self.cx().const_i8(Ordering::Equal as i8),
+            );
+            self.select(is_lt, self.cx().const_i8(Ordering::Less as i8), ge)
+        }
     }
 
     fn memcpy(
diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index 91d11ba317a..ab5d5c03e81 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -344,7 +344,6 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   Options.EmitStackSizeSection = EmitStackSizeSection;
 
   if (ArgsCstrBuff != nullptr) {
-#if LLVM_VERSION_GE(20, 0)
     size_t buffer_offset = 0;
     assert(ArgsCstrBuff[ArgsCstrBuffLen - 1] == '\0');
     auto Arg0 = std::string(ArgsCstrBuff);
@@ -362,33 +361,6 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     OS.flush();
     Options.MCOptions.Argv0 = Arg0;
     Options.MCOptions.CommandlineArgs = CommandlineArgs;
-#else
-    size_t buffer_offset = 0;
-    assert(ArgsCstrBuff[ArgsCstrBuffLen - 1] == '\0');
-
-    const size_t arg0_len = std::strlen(ArgsCstrBuff);
-    char *arg0 = new char[arg0_len + 1];
-    memcpy(arg0, ArgsCstrBuff, arg0_len);
-    arg0[arg0_len] = '\0';
-    buffer_offset += arg0_len + 1;
-
-    const size_t num_cmd_arg_strings = std::count(
-        &ArgsCstrBuff[buffer_offset], &ArgsCstrBuff[ArgsCstrBuffLen], '\0');
-
-    std::string *cmd_arg_strings = new std::string[num_cmd_arg_strings];
-    for (size_t i = 0; i < num_cmd_arg_strings; ++i) {
-      assert(buffer_offset < ArgsCstrBuffLen);
-      const size_t len = std::strlen(ArgsCstrBuff + buffer_offset);
-      cmd_arg_strings[i] = std::string(&ArgsCstrBuff[buffer_offset], len);
-      buffer_offset += len + 1;
-    }
-
-    assert(buffer_offset == ArgsCstrBuffLen);
-
-    Options.MCOptions.Argv0 = arg0;
-    Options.MCOptions.CommandLineArgs =
-        llvm::ArrayRef<std::string>(cmd_arg_strings, num_cmd_arg_strings);
-#endif
   }
 
 #if LLVM_VERSION_GE(21, 0)
@@ -402,12 +374,6 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
 }
 
 extern "C" void LLVMRustDisposeTargetMachine(LLVMTargetMachineRef TM) {
-#if LLVM_VERSION_LT(20, 0)
-  MCTargetOptions &MCOptions = unwrap(TM)->Options.MCOptions;
-  delete[] MCOptions.Argv0;
-  delete[] MCOptions.CommandLineArgs.data();
-#endif
-
   delete unwrap(TM);
 }
 
@@ -688,14 +654,9 @@ extern "C" LLVMRustResult LLVMRustOptimize(
   // the PassBuilder does not create a pipeline.
   std::vector<std::function<void(ModulePassManager &, OptimizationLevel)>>
       PipelineStartEPCallbacks;
-#if LLVM_VERSION_GE(20, 0)
   std::vector<std::function<void(ModulePassManager &, OptimizationLevel,
                                  ThinOrFullLTOPhase)>>
       OptimizerLastEPCallbacks;
-#else
-  std::vector<std::function<void(ModulePassManager &, OptimizationLevel)>>
-      OptimizerLastEPCallbacks;
-#endif
 
   if (!IsLinkerPluginLTO && SanitizerOptions && SanitizerOptions->SanitizeCFI &&
       !NoPrepopulatePasses) {
@@ -747,12 +708,8 @@ extern "C" LLVMRustResult LLVMRustOptimize(
           SanitizerOptions->SanitizeDataFlowABIList +
               SanitizerOptions->SanitizeDataFlowABIListLen);
       OptimizerLastEPCallbacks.push_back(
-#if LLVM_VERSION_GE(20, 0)
           [ABIListFiles](ModulePassManager &MPM, OptimizationLevel Level,
                          ThinOrFullLTOPhase phase) {
-#else
-          [ABIListFiles](ModulePassManager &MPM, OptimizationLevel Level) {
-#endif
             MPM.addPass(DataFlowSanitizerPass(ABIListFiles));
           });
     }
@@ -763,66 +720,48 @@ extern "C" LLVMRustResult LLVMRustOptimize(
           SanitizerOptions->SanitizeMemoryRecover,
           /*CompileKernel=*/false,
           /*EagerChecks=*/true);
-      OptimizerLastEPCallbacks.push_back(
-#if LLVM_VERSION_GE(20, 0)
-          [Options](ModulePassManager &MPM, OptimizationLevel Level,
-                    ThinOrFullLTOPhase phase) {
-#else
-          [Options](ModulePassManager &MPM, OptimizationLevel Level) {
-#endif
-            MPM.addPass(MemorySanitizerPass(Options));
-          });
+      OptimizerLastEPCallbacks.push_back([Options](ModulePassManager &MPM,
+                                                   OptimizationLevel Level,
+                                                   ThinOrFullLTOPhase phase) {
+        MPM.addPass(MemorySanitizerPass(Options));
+      });
     }
 
     if (SanitizerOptions->SanitizeThread) {
-      OptimizerLastEPCallbacks.push_back(
-#if LLVM_VERSION_GE(20, 0)
-          [](ModulePassManager &MPM, OptimizationLevel Level,
-             ThinOrFullLTOPhase phase) {
-#else
-          [](ModulePassManager &MPM, OptimizationLevel Level) {
-#endif
-            MPM.addPass(ModuleThreadSanitizerPass());
-            MPM.addPass(
-                createModuleToFunctionPassAdaptor(ThreadSanitizerPass()));
-          });
+      OptimizerLastEPCallbacks.push_back([](ModulePassManager &MPM,
+                                            OptimizationLevel Level,
+                                            ThinOrFullLTOPhase phase) {
+        MPM.addPass(ModuleThreadSanitizerPass());
+        MPM.addPass(createModuleToFunctionPassAdaptor(ThreadSanitizerPass()));
+      });
     }
 
     if (SanitizerOptions->SanitizeAddress ||
         SanitizerOptions->SanitizeKernelAddress) {
-      OptimizerLastEPCallbacks.push_back(
-#if LLVM_VERSION_GE(20, 0)
-          [SanitizerOptions, TM](ModulePassManager &MPM,
-                                 OptimizationLevel Level,
-                                 ThinOrFullLTOPhase phase) {
-#else
-          [SanitizerOptions, TM](ModulePassManager &MPM,
-                                 OptimizationLevel Level) {
-#endif
-            auto CompileKernel = SanitizerOptions->SanitizeKernelAddress;
-            AddressSanitizerOptions opts = AddressSanitizerOptions{
-                CompileKernel,
-                SanitizerOptions->SanitizeAddressRecover ||
-                    SanitizerOptions->SanitizeKernelAddressRecover,
-                /*UseAfterScope=*/true,
-                AsanDetectStackUseAfterReturnMode::Runtime,
-            };
-            MPM.addPass(AddressSanitizerPass(
-                opts,
-                /*UseGlobalGC*/ true,
-                // UseOdrIndicator should be false on windows machines
-                // https://reviews.llvm.org/D137227
-                !TM->getTargetTriple().isOSWindows()));
-          });
+      OptimizerLastEPCallbacks.push_back([SanitizerOptions,
+                                          TM](ModulePassManager &MPM,
+                                              OptimizationLevel Level,
+                                              ThinOrFullLTOPhase phase) {
+        auto CompileKernel = SanitizerOptions->SanitizeKernelAddress;
+        AddressSanitizerOptions opts = AddressSanitizerOptions{
+            CompileKernel,
+            SanitizerOptions->SanitizeAddressRecover ||
+                SanitizerOptions->SanitizeKernelAddressRecover,
+            /*UseAfterScope=*/true,
+            AsanDetectStackUseAfterReturnMode::Runtime,
+        };
+        MPM.addPass(
+            AddressSanitizerPass(opts,
+                                 /*UseGlobalGC*/ true,
+                                 // UseOdrIndicator should be false on windows
+                                 // machines https://reviews.llvm.org/D137227
+                                 !TM->getTargetTriple().isOSWindows()));
+      });
     }
     if (SanitizerOptions->SanitizeHWAddress) {
       OptimizerLastEPCallbacks.push_back(
-#if LLVM_VERSION_GE(20, 0)
           [SanitizerOptions](ModulePassManager &MPM, OptimizationLevel Level,
                              ThinOrFullLTOPhase phase) {
-#else
-          [SanitizerOptions](ModulePassManager &MPM, OptimizationLevel Level) {
-#endif
             HWAddressSanitizerOptions opts(
                 /*CompileKernel=*/false,
                 SanitizerOptions->SanitizeHWAddressRecover,
@@ -904,11 +843,7 @@ extern "C" LLVMRustResult LLVMRustOptimize(
     for (const auto &C : PipelineStartEPCallbacks)
       C(MPM, OptLevel);
     for (const auto &C : OptimizerLastEPCallbacks)
-#if LLVM_VERSION_GE(20, 0)
       C(MPM, OptLevel, ThinOrFullLTOPhase::None);
-#else
-      C(MPM, OptLevel);
-#endif
   }
 
   if (ExtraPassesLen) {
@@ -1185,11 +1120,7 @@ struct LLVMRustThinLTOData {
 
   // Not 100% sure what these are, but they impact what's internalized and
   // what's inlined across modules, I believe.
-#if LLVM_VERSION_GE(20, 0)
   FunctionImporter::ImportListsTy ImportLists;
-#else
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists;
-#endif
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists;
   DenseMap<StringRef, GVSummaryMapTy> ModuleToDefinedGVSummaries;
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
@@ -1531,13 +1462,8 @@ extern "C" void LLVMRustComputeLTOCacheKey(RustStringRef KeyOut,
   const auto &ExportList = Data->ExportLists.lookup(ModId);
   const auto &ResolvedODR = Data->ResolvedODR.lookup(ModId);
   const auto &DefinedGlobals = Data->ModuleToDefinedGVSummaries.lookup(ModId);
-#if LLVM_VERSION_GE(20, 0)
   DenseSet<GlobalValue::GUID> CfiFunctionDefs;
   DenseSet<GlobalValue::GUID> CfiFunctionDecls;
-#else
-  std::set<GlobalValue::GUID> CfiFunctionDefs;
-  std::set<GlobalValue::GUID> CfiFunctionDecls;
-#endif
 
   // Based on the 'InProcessThinBackend' constructor in LLVM
 #if LLVM_VERSION_GE(21, 0)
@@ -1556,15 +1482,9 @@ extern "C" void LLVMRustComputeLTOCacheKey(RustStringRef KeyOut,
         GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(Name)));
 #endif
 
-#if LLVM_VERSION_GE(20, 0)
   Key = llvm::computeLTOCacheKey(conf, Data->Index, ModId, ImportList,
                                  ExportList, ResolvedODR, DefinedGlobals,
                                  CfiFunctionDefs, CfiFunctionDecls);
-#else
-  llvm::computeLTOCacheKey(Key, conf, Data->Index, ModId, ImportList,
-                           ExportList, ResolvedODR, DefinedGlobals,
-                           CfiFunctionDefs, CfiFunctionDecls);
-#endif
 
   auto OS = RawRustStringOstream(KeyOut);
   OS << Key.str();