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/calls.go

@@ -35,6 +35,9 @@ const (
 
 	// Whether this is a readonly parameter (for example, a string pointer).
 	paramIsReadonly
+
+	// Whether this parameter is passed through backing storage.
+	paramIsIndirect
 )
 
 // createRuntimeCallCommon creates a runtime call. Use createRuntimeCall or
@@ -102,6 +105,14 @@ func (b *builder) createInvoke(fnType llvm.Type, fn llvm.Value, args []llvm.Valu
 // Expand an argument type to a list that can be used in a function call
 // parameter list.
 func (c *compilerContext) expandFormalParamType(t llvm.Type, name string, goType types.Type) []paramInfo {
+	if c.isIndirectAggregate(t) {
+		return []paramInfo{{
+			llvmType: c.dataPtrType,
+			name:     name,
+			elemSize: c.targetData.TypeAllocSize(t),
+			flags:    paramIsGoParam | paramIsReadonly | paramIsIndirect,
+		}}
+	}
 	return c.expandDirectFormalParamType(t, name, goType)
 }
 
@@ -119,6 +130,38 @@ func (c *compilerContext) expandDirectFormalParamType(t llvm.Type, name string,
 	return []paramInfo{c.getParamInfo(t, name, goType)}
 }
 
+func (c *compilerContext) storedParamType(t llvm.Type, exported bool) llvm.Type {
+	if c.isIndirectParam(t, exported) {
+		return c.dataPtrType
+	}
+	return t
+}
+
+func (c *compilerContext) isIndirectParam(t llvm.Type, exported bool) bool {
+	return !exported && c.isIndirectAggregate(t)
+}
+
+func (b *builder) appendStoredValueTypes(valueTypes []llvm.Type, values []ssa.Value, exported bool) []llvm.Type {
+	for _, value := range values {
+		valueTypes = append(valueTypes, b.storedParamType(b.getLLVMType(value.Type()), exported))
+	}
+	return valueTypes
+}
+
+func (b *builder) appendStoredParamTypes(valueTypes []llvm.Type, params []*types.Var, exported bool) []llvm.Type {
+	for _, param := range params {
+		valueTypes = append(valueTypes, b.storedParamType(b.getLLVMType(param.Type()), exported))
+	}
+	return valueTypes
+}
+
+func (b *builder) prependIndirectResult(sig *types.Signature, exported bool, params []llvm.Value, name string) []llvm.Value {
+	if resultType, indirect := b.hasIndirectResult(sig); !exported && indirect {
+		return append([]llvm.Value{b.createIndirectStorage(resultType, name)}, params...)
+	}
+	return params
+}
+
 // expandFormalParamOffsets returns a list of offsets from the start of an
 // object of type t after it would have been split up by expandFormalParam. This
 // is useful for debug information, where it is necessary to know the offset