We may visit a call that uses an alloca multiple times in callUsesLocalStack, sometimes with IsNocapture true and sometimes with IsNocapture false. We accidentally skipped work we needed to do in the IsNocapture=false case if we were called with IsNocapture=true the first time. Fixes PR20405!

llvm-svn: 213726

llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp

@@ -227,12 +227,10 @@ struct AllocaDerivedValueTracker {
   }
 
   void callUsesLocalStack(CallSite CS, bool IsNocapture) {
-    // Add it to the list of alloca users. If it's already there, skip further
-    // processing.
-    if (!AllocaUsers.insert(CS.getInstruction()))
-      return;
+    // Add it to the list of alloca users.
+    AllocaUsers.insert(CS.getInstruction());
 
-    // If it's nocapture then it can't capture the alloca.
+    // If it's nocapture then it can't capture this alloca.
     if (IsNocapture)
       return;
 

llvm/test/Transforms/TailCallElim/basic.ll

@@ -174,3 +174,17 @@ if.end:
 return:
   ret void
 }
+
+declare void @test11_helper1(i8** nocapture, i8*)
+declare void @test11_helper2(i8*)
+define void @test11() {
+; CHECK-LABEL: @test11
+; CHECK-NOT: tail
+  %a = alloca i8*
+  %b = alloca i8
+  call void @test11_helper1(i8** %a, i8* %b)  ; a = &b
+  %c = load i8** %a
+  call void @test11_helper2(i8* %c)
+; CHECK: call void @test11_helper2
+  ret void
+}