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compiler: work around AVR atomics bugs

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The AVR backend has several critical atomics bugs.
This change invokes libcalls for all atomic operations on AVR.
Now `testdata/atomic.go` compiles and runs correctly.
This commit is contained in:
Nia Waldvogel
2022-01-13 14:02:34 -05:00
committed by Ron Evans
parent b2ef7299b7
commit e2178ce682
3 changed files with 53 additions and 1 deletions
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compiler/atomic.go
+32
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@@ -1,6 +1,7 @@
package compiler
import (
"fmt"
"strings"
"golang.org/x/tools/go/ssa"
@@ -16,6 +17,20 @@ func (b *builder) createAtomicOp(call *ssa.CallCommon) (llvm.Value, bool) {
case "AddInt32", "AddInt64", "AddUint32", "AddUint64", "AddUintptr":
ptr := b.getValue(call.Args[0])
val := b.getValue(call.Args[1])
if strings.HasPrefix(b.Triple, "avr") {
// AtomicRMW does not work on AVR as intended:
// - There are some register allocation issues (fixed by https://reviews.llvm.org/D97127 which is not yet in a usable LLVM release)
// - The result is the new value instead of the old value
vType := val.Type()
name := fmt.Sprintf("__sync_fetch_and_add_%d", vType.IntTypeWidth()/8)
fn := b.mod.NamedFunction(name)
if fn.IsNil() {
fn = llvm.AddFunction(b.mod, name, llvm.FunctionType(vType, []llvm.Type{ptr.Type(), vType}, false))
}
oldVal := b.createCall(fn, []llvm.Value{ptr, val}, "")
// Return the new value, not the original value returned.
return b.CreateAdd(oldVal, val, ""), true
}
oldVal := b.CreateAtomicRMW(llvm.AtomicRMWBinOpAdd, ptr, val, llvm.AtomicOrderingSequentiallyConsistent, true)
// Return the new value, not the original value returned by atomicrmw.
return b.CreateAdd(oldVal, val, ""), true
@@ -73,6 +88,23 @@ func (b *builder) createAtomicOp(call *ssa.CallCommon) (llvm.Value, bool) {
case "StoreInt32", "StoreInt64", "StoreUint32", "StoreUint64", "StoreUintptr", "StorePointer":
ptr := b.getValue(call.Args[0])
val := b.getValue(call.Args[1])
if strings.HasPrefix(b.Triple, "avr") {
// SelectionDAGBuilder is currently missing the "are unaligned atomics allowed" check for stores.
vType := val.Type()
isPointer := vType.TypeKind() == llvm.PointerTypeKind
if isPointer {
// libcalls only supports integers, so cast to an integer.
vType = b.uintptrType
val = b.CreatePtrToInt(val, vType, "")
ptr = b.CreateBitCast(ptr, llvm.PointerType(vType, 0), "")
}
name := fmt.Sprintf("__atomic_store_%d", vType.IntTypeWidth()/8)
fn := b.mod.NamedFunction(name)
if fn.IsNil() {
fn = llvm.AddFunction(b.mod, name, llvm.FunctionType(vType, []llvm.Type{ptr.Type(), vType, b.uintptrType}, false))
}
return b.createCall(fn, []llvm.Value{ptr, val, llvm.ConstInt(b.uintptrType, 5, false)}, ""), true
}
store := b.CreateStore(val, ptr)
store.SetOrdering(llvm.AtomicOrderingSequentiallyConsistent)
store.SetAlignment(b.targetData.PrefTypeAlignment(val.Type())) // required