[asan] In llvm.asan.globals, allow entries to be non-GlobalVariable and skip over them

Looks like there are valid reasons why we need to allow bitcasts in llvm.asan.globals, see discussion at apple/swift-llvm#133. Let's look through bitcasts when iterating over entries in the llvm.asan.globals list.

Differential Revision: https://reviews.llvm.org/D55794

llvm-svn: 349544

Author: kubamracek

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -441,8 +441,11 @@ class GlobalsMetadata {
     for (auto MDN : Globals->operands()) {
       // Metadata node contains the global and the fields of "Entry".
       assert(MDN->getNumOperands() == 5);
-      auto *GV = mdconst::extract_or_null<GlobalVariable>(MDN->getOperand(0));
+      auto *V = mdconst::extract_or_null<Constant>(MDN->getOperand(0));
       // The optimizer may optimize away a global entirely.
+      if (!V) continue;
+      auto *StrippedV = V->stripPointerCasts();
+      auto *GV = dyn_cast<GlobalVariable>(StrippedV);
       if (!GV) continue;
       // We can already have an entry for GV if it was merged with another
       // global.

llvm/test/Instrumentation/AddressSanitizer/global_metadata_bitcasts.ll

@@ -0,0 +1,13 @@
+; Test that the compiler doesn't crash when the llvm.asan.globals containts
+; an entry that points to a BitCast instruction.
+
+; RUN: opt < %s -asan -asan-module -asan-globals-live-support=1 -S
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+@g = global [1 x i32] zeroinitializer, align 4
+
+!llvm.asan.globals = !{!0, !1}
+!0 = !{[1 x i32]* @g, null, !"name", i1 false, i1 false}
+!1 = !{i8* bitcast ([1 x i32]* @g to i8*), null, !"name", i1 false, i1 false}