[5.3] SIL: fix memory behavior of global_addr for globals with non-fixed layout.

lib/SIL/IR/SILInstruction.cpp

@@ -1002,6 +1002,22 @@ SILInstruction::MemoryBehavior SILInstruction::getMemoryBehavior() const {
     }
   }
 
+  if (auto *ga = dyn_cast<GlobalAddrInst>(this)) {
+    // Global variables with resilient types might be allocated into a buffer
+    // and not statically in the data segment.
+    // In this case, the global_addr depends on alloc_global being executed
+    // first. We model this by letting global_addr have a side effect.
+    // It prevents e.g. LICM to move a global_addr out of a loop while keeping
+    // the alloc_global inside the loop.
+    SILModule &M = ga->getFunction()->getModule();
+    auto expansion = TypeExpansionContext::maximal(M.getAssociatedContext(),
+                                                   M.isWholeModule());
+    const TypeLowering &tl =
+      M.Types.getTypeLowering(ga->getType().getObjectType(), expansion);
+    return tl.isFixedABI() ? MemoryBehavior::None :
+                             MemoryBehavior::MayHaveSideEffects;
+  }
+
   switch (getKind()) {
 #define FULL_INST(CLASS, TEXTUALNAME, PARENT, MEMBEHAVIOR, RELEASINGBEHAVIOR)  \
   case SILInstructionKind::CLASS:                                              \

test/SILOptimizer/Inputs/licm_and_global_addr/main.swift

@@ -0,0 +1,2 @@
+
+testit(3)

test/SILOptimizer/Inputs/licm_and_global_addr/test.swift

@@ -0,0 +1,17 @@
+
+public struct Abc {
+  public var a = 1
+  public var b = 2
+  public var c = 3
+  public var d = 4
+
+  public init() { }
+
+  public mutating func printit() {
+    print(a)
+  }
+}
+
+public func unknown() {
+}
+

test/SILOptimizer/licm_and_global_addr.swift

@@ -0,0 +1,29 @@
+// RUN: %empty-directory(%t) 
+// RUN: %target-build-swift %S/Inputs/licm_and_global_addr/test.swift -parse-as-library -wmo -enable-library-evolution -module-name=Test -emit-module -emit-module-path=%t/Test.swiftmodule -c -o %t/test.o
+// RUN: %target-build-swift -O %S/Inputs/licm_and_global_addr/main.swift %s -I%t %t/test.o -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: executable_test
+
+import Test
+
+// Check that LICM does not move a global_addr above an alloc_global in case
+// the global might be dynamically allocated.
+
+// The type Abc is resilient and > 3 words. So it is allocated dynamically in a buffer.
+var a = Abc()
+
+@inline(never)
+func testit(_ n: Int) {
+  for _ in 0..<n {
+    // Prevent hoisting the initialization of 'a', 
+    // which would defeat the purpose of the test.
+    unknown()
+
+// CHECK: 1
+// CHECK: 1
+// CHECK: 1
+    a.printit()
+  }
+}
+