[GlobalsAA] Don't assume anything about functions that may be overridden

Weak linkage and friends allow a symbol to be overriden outside the
code generator's model, so GlobalsAA shouldn't assume that anything it
can compute about such a symbol is valid.

llvm-svn: 250156

2 files changed, 26 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
index 40915f45dff..be5d384c435 100644
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -480,8 +480,8 @@ void GlobalsAAResult::AnalyzeCallGraph(CallGraph &CG, Module &M) {
     const std::vector<CallGraphNode *> &SCC = *I;
     assert(!SCC.empty() && "SCC with no functions?");
 
-    if (!SCC[0]->getFunction()) {
-      // Calls externally - can't say anything useful.  Remove any existing
+    if (!SCC[0]->getFunction() || SCC[0]->getFunction()->mayBeOverridden()) {
+      // Calls externally or is weak - can't say anything useful. Remove any existing
       // function records (may have been created when scanning globals).
       for (auto *Node : SCC)
         FunctionInfos.erase(Node->getFunction());
diff --git a/llvm/test/Analysis/GlobalsModRef/weak-interposition.ll b/llvm/test/Analysis/GlobalsModRef/weak-interposition.ll
new file mode 100644
index 00000000000..091aa74d521
--- /dev/null
+++ b/llvm/test/Analysis/GlobalsModRef/weak-interposition.ll
@@ -0,0 +1,24 @@
+; RUN: opt -S -O1 -enable-non-lto-gmr=true < %s | FileCheck %s
+
+@a = common global i32 0, align 4
+
+; @hook_me is weak, so GMR must not eliminate the reload of @a in @f,
+; even though @hook_me doesn't mod or ref @a.
+
+; Function Attrs: nounwind ssp uwtable
+define weak i32 @hook_me() {
+  ret i32 0
+}
+
+; Function Attrs: nounwind ssp uwtable
+define i32 @f() {
+  %1 = alloca i32, align 4
+  store i32 4, i32* @a, align 4
+  %2 = call i32 @hook_me()
+  ; CHECK: load i32, i32* @a, align 4
+  %3 = load i32, i32* @a, align 4
+  %4 = add nsw i32 %3, %2
+  store i32 %4, i32* @a, align 4
+  %5 = load i32, i32* %1
+  ret i32 %5
+}