[GlobalsAA] An indirect global that is initialized is not fair game

When checking if an indirect global (a global with pointer type) is only assigned by allocation functions, first check if the global is itself initialized. If it is, it's not only assigned by allocation functions.

This fixes PR25309. Thanks to David Majnemer for reducing the test case!

llvm-svn: 251508

3 files changed, 34 insertions, 2 deletions

diff --git a/llvm/include/llvm/Analysis/GlobalsModRef.h b/llvm/include/llvm/Analysis/GlobalsModRef.h
index d45e4d430ae..bcd102e7ded 100644
--- a/llvm/include/llvm/Analysis/GlobalsModRef.h
+++ b/llvm/include/llvm/Analysis/GlobalsModRef.h
@@ -107,7 +107,7 @@ private:
                             SmallPtrSetImpl<Function *> *Readers = nullptr,
                             SmallPtrSetImpl<Function *> *Writers = nullptr,
                             GlobalValue *OkayStoreDest = nullptr);
-  bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
+  bool AnalyzeIndirectGlobalMemory(GlobalVariable *GV);
   void CollectSCCMembership(CallGraph &CG);
 
   bool isNonEscapingGlobalNoAlias(const GlobalValue *GV, const Value *V);
diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
index 3b808e371db..c809ff83457 100644
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -395,11 +395,16 @@ bool GlobalsAAResult::AnalyzeUsesOfPointer(Value *V,
 /// Further, all loads out of GV must directly use the memory, not store the
 /// pointer somewhere.  If this is true, we consider the memory pointed to by
 /// GV to be owned by GV and can disambiguate other pointers from it.
-bool GlobalsAAResult::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
+bool GlobalsAAResult::AnalyzeIndirectGlobalMemory(GlobalVariable *GV) {
   // Keep track of values related to the allocation of the memory, f.e. the
   // value produced by the malloc call and any casts.
   std::vector<Value *> AllocRelatedValues;
 
+  // If the initializer is a valid pointer, bail.
+  if (Constant *C = GV->getInitializer())
+    if (!C->isNullValue())
+      return false;
+    
   // Walk the user list of the global.  If we find anything other than a direct
   // load or store, bail out.
   for (User *U : GV->users()) {
diff --git a/llvm/test/Analysis/GlobalsModRef/pr25309.ll b/llvm/test/Analysis/GlobalsModRef/pr25309.ll
new file mode 100644
index 00000000000..ce3b498c802
--- /dev/null
+++ b/llvm/test/Analysis/GlobalsModRef/pr25309.ll
@@ -0,0 +1,27 @@
+; RUN: opt -globals-aa -gvn < %s -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; @o and @m are initialized to @i, so they should not be classed as
+; indirect globals referring only to allocation functions.
+@o = internal global i32* @i, align 8
+@m = internal global i32* @i, align 8
+@i = internal global i32 0, align 4
+
+; CHECK-LABEL: @f
+define i1 @f() {
+entry:
+  %0 = load i32*, i32** @o, align 8
+  store i32 0, i32* %0, align 4
+  %1 = load volatile i32*, i32** @m, align 8
+  store i32 1, i32* %1, align 4
+  ; CHECK: %[[a:.*]] = load i32*
+  %2 = load i32*, i32** @o, align 8
+  ; CHECK: %[[b:.*]] = load i32, i32* %[[a]]
+  %3 = load i32, i32* %2, align 4
+  ; CHECK: %[[c:.*]] = icmp ne i32 %[[b]], 0
+  %tobool.i = icmp ne i32 %3, 0
+  ; CHECK: ret i1 %[[c]]
+  ret i1 %tobool.i
+}
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