Don't shrink atomic ops to bool in GlobalOpt.

LLVM IR doesn't currently allow atomic bool load/store operations, and the
transformation is dubious anyway because it isn't profitable on all platforms.

PR17163.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190357 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/GlobalOpt.cpp

@@ -2046,11 +2046,14 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
 
     // Otherwise, if the global was not a boolean, we can shrink it to be a
     // boolean.
-    if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
-      if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
-        ++NumShrunkToBool;
-        return true;
+    if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
+      if (GS.Ordering == NotAtomic) {
+        if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
+          ++NumShrunkToBool;
+          return true;
+        }
       }
+    }
   }
 
   return false;

test/Transforms/GlobalOpt/atomic.ll

@@ -1,10 +1,25 @@
 ; RUN: opt -globalopt < %s -S -o - | FileCheck %s
 
 @GV1 = internal global i64 1
+@GV2 = internal global i32 0
+
 ; CHECK: @GV1 = internal unnamed_addr constant i64 1
+; CHECK: @GV2 = internal unnamed_addr global i32 0
 
 define void @test1() {
 entry:
   %0 = load atomic i8* bitcast (i64* @GV1 to i8*) acquire, align 8
   ret void
 }
+
+; PR17163
+define void @test2a() {
+entry:
+  store atomic i32 10, i32* @GV2 seq_cst, align 4
+  ret void
+}
+define i32 @test2b() {
+entry:
+  %atomic-load = load atomic i32* @GV2 seq_cst, align 4
+  ret i32 %atomic-load
+}