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/symbol.go

@@ -79,13 +79,27 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 		return llvmFn.GlobalValueType(), llvmFn
 	}
 
-	retType := c.getLLVMResultType(fn.Signature)
+	retType, indirectResult := c.hasIndirectResult(fn.Signature)
+	if info.exported {
+		indirectResult = false
+	}
 
 	var paramInfos []paramInfo
+	if indirectResult {
+		paramInfos = append(paramInfos, paramInfo{
+			llvmType: c.dataPtrType,
+			name:     "return",
+			elemSize: c.targetData.TypeAllocSize(retType),
+		})
+		retType = c.ctx.VoidType()
+	}
 	for _, param := range getParams(fn.Signature) {
 		paramType := c.getLLVMType(param.Type())
-		paramFragmentInfos := c.expandFormalParamType(paramType, param.Name(), param.Type())
-		paramInfos = append(paramInfos, paramFragmentInfos...)
+		if info.exported {
+			paramInfos = append(paramInfos, c.expandDirectFormalParamType(paramType, param.Name(), param.Type())...)
+		} else {
+			paramInfos = append(paramInfos, c.expandFormalParamType(paramType, param.Name(), param.Type())...)
+		}
 	}
 
 	// Add an extra parameter as the function context. This context is used in
@@ -95,12 +109,20 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
 	}
 
 	var paramTypes []llvm.Type
+	hasIndirectABI := indirectResult
 	for _, info := range paramInfos {
 		paramTypes = append(paramTypes, info.llvmType)
+		hasIndirectABI = hasIndirectABI || info.flags&paramIsIndirect != 0
 	}
 
 	fnType := llvm.FunctionType(retType, paramTypes, info.variadic)
 	llvmFn = llvm.AddFunction(c.mod, info.linkName, fnType)
+	if hasIndirectABI {
+		// Argument promotion only rewrites functions whose uses are all direct
+		// calls. Keep an address use so LLVM cannot reconstruct the large
+		// aggregate signature that this ABI exists to avoid.
+		llvmutil.AppendToGlobal(c.mod, "llvm.used", llvmFn)
+	}
 	if strings.HasPrefix(c.Triple, "wasm") {
 		// C functions without prototypes like this:
 		//   void foo();