compiler: pass large aggregates by pointer

LLVM ComputeValueVTs recursively expands arrays and structs into one
value type per scalar leaf. SelectionDAG call lowering allocates data
structures proportional to this count, which makes very large values
exhaust memory or crash LLVM.

Count scalar leaves and use pointers for internal parameters and results
when the count exceeds 1024. A result pointer is the first parameter,
and aggregate parameters point to read-only memory. Exported function
types are unchanged.

Keep these SSA values in memory and copy them with memcpy when needed.
Handle calls, interfaces, maps, channels, selects, defers, goroutines,
phis, and multiple results. Update the expected compiler IR and re-enable
the native compress/flate tests.

compiler/channel.go

@@ -34,11 +34,11 @@ func (b *builder) createChanSend(instr *ssa.Send) {
 	// store value-to-send
 	valueType := b.getLLVMType(instr.X.Type())
 	isZeroSize := b.targetData.TypeAllocSize(valueType) == 0
-	var valueAlloca, valueAllocaSize llvm.Value
+	var storage valueStorage
 	if isZeroSize {
-		valueAlloca = llvm.ConstNull(b.dataPtrType)
+		storage.ptr = llvm.ConstNull(b.dataPtrType)
 	} else {
-		valueAlloca, valueAllocaSize = b.getValueStorage(instr.X, "chan.value")
+		storage = b.getValueStorage(instr.X, "chan.value")
 	}
 
 	// Allocate buffer for the channel operation.
@@ -46,15 +46,13 @@ func (b *builder) createChanSend(instr *ssa.Send) {
 	channelOpAlloca, channelOpAllocaSize := b.createTemporaryAlloca(channelOp, "chan.op")
 
 	// Do the send.
-	b.createRuntimeInvoke("chanSend", []llvm.Value{ch, valueAlloca, channelOpAlloca}, "")
+	b.createRuntimeInvoke("chanSend", []llvm.Value{ch, storage.ptr, channelOpAlloca}, "")
 
 	// End the lifetime of the allocas.
 	// This also works around a bug in CoroSplit, at least in LLVM 8:
 	// https://bugs.llvm.org/show_bug.cgi?id=41742
 	b.emitLifetimeEnd(channelOpAlloca, channelOpAllocaSize)
-	if !isZeroSize {
-		b.emitLifetimeEnd(valueAlloca, valueAllocaSize)
-	}
+	b.endValueStorage(storage)
 }
 
 // createChanRecv emits a pseudo chan receive operation. It is lowered to the
@@ -63,6 +61,7 @@ func (b *builder) createChanRecv(unop *ssa.UnOp) llvm.Value {
 	valueType := b.getLLVMType(unop.X.Type().Underlying().(*types.Chan).Elem())
 	ch := b.getValue(unop.X, getPos(unop))
 
+	// Allocate memory to receive into.
 	result := b.createRuntimeValueResult(valueType, unop.CommaOk, true, "chan")
 
 	// Allocate buffer for the channel operation.
@@ -261,6 +260,9 @@ func (b *builder) getChanSelectResult(expr *ssa.Extract) llvm.Value {
 
 func (b *builder) getSelectSendStorage(value ssa.Value) llvm.Value {
 	typ := b.getLLVMType(value.Type())
+	if b.isIndirectAggregate(typ) {
+		return b.getValuePointer(value)
+	}
 	llvmValue := b.getValue(value, getPos(value))
 	ptr := llvmutil.CreateEntryBlockAlloca(b.Builder, typ, "select.send.value")
 	b.CreateStore(llvmValue, ptr)