Disallow non-constant globals with @_section attribute

Author: kubamracek

include/swift/AST/DiagnosticsSIL.def

@@ -332,6 +332,8 @@ ERROR(performance_unknown_callees,none,
       "called function is not known at compile time and can have unpredictable performance", ())
 ERROR(performance_callee_unavailable,none,
       "called function is not available in this module and can have unpredictable performance", ())
+ERROR(section_attr_on_non_const_global,none,
+      "global variable must be a compile-time constant to use @_section attribute", ())
 NOTE(performance_called_from,none,
       "called from here", ())
 

lib/SILOptimizer/Mandatory/PerformanceDiagnostics.cpp

@@ -476,6 +476,14 @@ class PerformanceDiagnosticsPass : public SILModuleTransform {
     SILModule *module = getModule();
 
     PerformanceDiagnostics diagnoser(*module, getAnalysis<BasicCalleeAnalysis>());
+
+    // Check that @_section is only on constant globals
+    for (SILGlobalVariable &g : module->getSILGlobals()) {
+      if (!g.getStaticInitializerValue() && g.getSectionAttr())
+        module->getASTContext().Diags.diagnose(
+            g.getDecl()->getLoc(), diag::section_attr_on_non_const_global);
+    }
+
     bool annotatedFunctionsFound = false;
 
     for (SILFunction &function : *module) {

test/IRGen/section_non_const.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -parse-as-library -emit-sil %s -o /dev/null -verify
+
+// REQUIRES: swift_in_compiler
+
+@_section("__TEXT,__mysection") var g0: Int = 1
+@_section("__TEXT,__mysection") var g1: (Int, Int) = (1, 2)
+@_section("__TEXT,__mysection") var g2: [Int] = [1, 2, 3] // expected-error {{global variable must be a compile-time constant to use @_section attribute}}
+@_section("__TEXT,__mysection") var g3: [Int:Int] = [:] // expected-error {{global variable must be a compile-time constant to use @_section attribute}}
+@_section("__TEXT,__mysection") var g4: UInt = 42
+@_section("__TEXT,__mysection") var g5: String = "hello" // expected-error {{global variable must be a compile-time constant to use @_section attribute}}
+@_section("__TEXT,__mysection") var g6: Any = 1 // expected-error {{global variable must be a compile-time constant to use @_section attribute}}
+@_section("__TEXT,__mysection") var g7: UInt8 = 42
+@_section("__TEXT,__mysection") var g8: Int = 5 * 5