all: initial support for LLVM 21

Author: aykevl

.circleci/config.yml

@@ -108,7 +108,7 @@ jobs:
       - image: golang:1.25-bullseye
     steps:
       - test-linux:
-          llvm: "20"
+          llvm: "21"
     resource_class: large
 
 workflows:

.github/workflows/build-macos.yml

@@ -117,7 +117,7 @@ jobs:
     runs-on: macos-latest
     strategy:
       matrix:
-        version: [16, 17, 18, 19, 20]
+        version: [16, 17, 18, 19, 20, 21]
     steps:
       - name: Set up Homebrew
         uses: Homebrew/actions/setup-homebrew@master
@@ -141,8 +141,8 @@ jobs:
       - name: Check binary
         run: tinygo version
       - name: Build TinyGo (default LLVM)
-        if: matrix.version == 20
+        if: matrix.version == 21
         run: go install
       - name: Check binary
-        if: matrix.version == 20
+        if: matrix.version == 21
         run: tinygo version

.github/workflows/sizediff-install-pkgs.sh

@@ -2,11 +2,11 @@
 # still works after checking out the dev branch (that is, when going from LLVM
 # 16 to LLVM 17 for example, both Clang 16 and Clang 17 are installed).
 
-echo 'deb https://apt.llvm.org/noble/ llvm-toolchain-noble-20 main' | sudo tee /etc/apt/sources.list.d/llvm.list
+echo 'deb https://apt.llvm.org/noble/ llvm-toolchain-noble-21 main' | sudo tee /etc/apt/sources.list.d/llvm.list
 wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
 sudo apt-get update
 sudo apt-get install --no-install-recommends -y \
-    llvm-20-dev \
-    clang-20 \
-    libclang-20-dev \
-    lld-20
+    llvm-21-dev \
+    clang-21 \
+    libclang-21-dev \
+    lld-21

cgo/libclang.go

@@ -21,6 +21,10 @@ import (
 )
 
 /*
+// Hide a warning in LLVM 21 that doesn't apply to us (appears to be a side
+// effect of how CGo processes C header files).
+#cgo CFLAGS: -Wno-deprecated-declarations
+
 #include <clang-c/Index.h> // If this fails, libclang headers aren't available. Please take a look here: https://tinygo.org/docs/guides/build/
 #include <llvm/Config/llvm-config.h>
 #include <stdlib.h>

cgo/libclang_config_llvm20.go

@@ -1,4 +1,4 @@
-//go:build !byollvm && !llvm15 && !llvm16 && !llvm17 && !llvm18 && !llvm19
+//go:build !byollvm && llvm20
 
 package cgo
 

cgo/libclang_config_llvm21.go

@@ -0,0 +1,15 @@
+//go:build !byollvm && !llvm15 && !llvm16 && !llvm17 && !llvm18 && !llvm19 && !llvm20
+
+package cgo
+
+/*
+#cgo linux        CFLAGS:  -I/usr/include/llvm-21 -I/usr/include/llvm-c-21 -I/usr/lib/llvm-21/include
+#cgo darwin,amd64 CFLAGS:  -I/usr/local/opt/llvm@21/include
+#cgo darwin,arm64 CFLAGS:  -I/opt/homebrew/opt/llvm@21/include
+#cgo freebsd      CFLAGS:  -I/usr/local/llvm21/include
+#cgo linux        LDFLAGS: -L/usr/lib/llvm-21/lib -lclang
+#cgo darwin,amd64 LDFLAGS: -L/usr/local/opt/llvm@21/lib -lclang
+#cgo darwin,arm64 LDFLAGS: -L/opt/homebrew/opt/llvm@21/lib -lclang
+#cgo freebsd      LDFLAGS: -L/usr/local/llvm21/lib -lclang
+*/
+import "C"

compiler/compiler.go

@@ -84,6 +84,7 @@ type compilerContext struct {
 	funcPtrType      llvm.Type // pointer in function address space (1 for AVR, 0 elsewhere)
 	funcPtrAddrSpace int
 	uintptrType      llvm.Type
+	nocaptureAttr    llvm.Attribute
 	program          *ssa.Program
 	diagnostics      []error
 	functionInfos    map[*ssa.Function]functionInfo
@@ -135,6 +136,13 @@ func newCompilerContext(moduleName string, machine llvm.TargetMachine, config *C
 	c.funcPtrType = dummyFunc.Type()
 	dummyFunc.EraseFromParentAsFunction()
 
+	// The attribute "nocapture" changed to "captures(none)" in LLVM 21.
+	if llvmutil.Version() < 21 {
+		c.nocaptureAttr = c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0)
+	} else {
+		c.nocaptureAttr = c.ctx.CreateEnumAttribute(llvm.AttributeKindID("captures"), 0)
+	}
+
 	return c
 }
 

compiler/symbol.go

@@ -139,8 +139,7 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 			// not.
 			// (It may be safe to add the nocapture parameter to the context
 			// parameter, but I'd like to stay on the safe side here).
-			nocapture := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0)
-			llvmFn.AddAttributeAtIndex(i+1, nocapture)
+			llvmFn.AddAttributeAtIndex(i+1, c.nocaptureAttr)
 		}
 	}
 
@@ -153,7 +152,7 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 		// Mark it as noreturn so LLVM can optimize away code.
 		llvmFn.AddFunctionAttr(c.ctx.CreateEnumAttribute(llvm.AttributeKindID("noreturn"), 0))
 	case "internal/abi.NoEscape":
-		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.nocaptureAttr)
 	case "runtime.alloc":
 		// Tell the optimizer that runtime.alloc is an allocator, meaning that it
 		// returns values that are never null and never alias to an existing value.
@@ -175,25 +174,25 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 	case "runtime.sliceAppend":
 		// Appending a slice will only read the to-be-appended slice, it won't
 		// be modified.
-		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(2, c.nocaptureAttr)
 		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
 	case "runtime.sliceCopy":
 		// Copying a slice won't capture any of the parameters.
 		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("writeonly"), 0))
-		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.nocaptureAttr)
 		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
-		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(2, c.nocaptureAttr)
 	case "runtime.stringFromBytes":
-		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.nocaptureAttr)
 		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
 	case "runtime.stringFromRunes":
-		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.nocaptureAttr)
 		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
 	case "runtime.trackPointer":
 		// This function is necessary for tracking pointers on the stack in a
 		// portable way (see gc_stack_portable.go). Indicate to the optimizer
 		// that the only thing we'll do is read the pointer.
-		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.nocaptureAttr)
 		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
 	case "__mulsi3", "__divmodsi4", "__udivmodsi4":
 		if strings.Split(c.Triple, "-")[0] == "avr" {
@@ -228,11 +227,9 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 
 			llvmFn.AddFunctionAttr(c.ctx.CreateStringAttribute("wasm-import-name", info.wasmName))
 		}
-		nocaptureKind := llvm.AttributeKindID("nocapture")
-		nocapture := c.ctx.CreateEnumAttribute(nocaptureKind, 0)
 		for i, typ := range paramTypes {
 			if typ.TypeKind() == llvm.PointerTypeKind {
-				llvmFn.AddAttributeAtIndex(i+1, nocapture)
+				llvmFn.AddAttributeAtIndex(i+1, c.nocaptureAttr)
 			}
 		}
 	}

flake.nix

@@ -48,11 +48,11 @@
           buildInputs = [
             # These dependencies are required for building tinygo (go install).
             go
-            llvmPackages_20.llvm
-            llvmPackages_20.libclang
+            llvmPackages_21.llvm
+            llvmPackages_21.libclang
             # Additional dependencies needed at runtime, for building and/or
             # flashing.
-            llvmPackages_20.lld
+            llvmPackages_21.lld
             avrdude
             binaryen
             # Additional dependencies needed for on-chip debugging.
@@ -68,7 +68,7 @@
             export MD5SUM=md5sum
 
             # Ugly hack to make the Clang resources directory available.
-            export GOFLAGS="\"-ldflags=-X github.com/tinygo-org/tinygo/goenv.clangResourceDir=${llvmPackages_20.clang.cc.lib}/lib/clang/20\" -tags=llvm20"
+            export GOFLAGS="\"-ldflags=-X github.com/tinygo-org/tinygo/goenv.clangResourceDir=${llvmPackages_21.clang.cc.lib}/lib/clang/21\""
           '';
         };
       }

go.mod

@@ -18,7 +18,7 @@ require (
 	golang.org/x/sys v0.30.0
 	golang.org/x/tools v0.30.0
 	gopkg.in/yaml.v2 v2.4.0
-	tinygo.org/x/go-llvm v0.0.0-20250422114502-b8f170971e74
+	tinygo.org/x/go-llvm v0.0.0-20250916101410-63740cfada08
 )
 
 require (