LowerAtomic: Don't skip optnone functions; atomic still need lowering (PR34020)

[hans]

Summary

The lowering isn't really an optimization, so optnone shouldn't make a difference. ARM relies on the pass running when using "-mthread-model single", because in that mode, it doesn't run AtomicExpand. See bug for more details.

[t.p.northover]

LGTM.

llvm/trunk/lib/Transforms/Scalar/LowerAtomic.cpp

 public:
   static char ID;
 
   LowerAtomicLegacyPass() : FunctionPass(ID) {
     initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnFunction(Function &F) override {
-    if (skipFunction(F))
-      return false;
+    // Don't skip optnone functions; atomics still need to be lowered.
     FunctionAnalysisManager DummyFAM;
     auto PA = Impl.run(F, DummyFAM);
     return !PA.areAllPreserved();
   }
 
 private:
   LowerAtomicPass Impl;
   };
 }
 
 char LowerAtomicLegacyPass::ID = 0;
 INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic",
                 "Lower atomic intrinsics to non-atomic form", false, false)
 
 Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); }

llvm/trunk/test/Feature/optnone-opt.ll

 
 ; Additional IR passes run at -O2 and higher.
 ; OPT-O2O3-DAG: Skipping pass 'Global Value Numbering'
 ; OPT-O2O3-DAG: Skipping pass 'SLP Vectorizer'
 
 ; Additional IR passes that opt doesn't turn on by default.
 ; OPT-MORE-DAG: Skipping pass 'Dead Code Elimination'
 ; OPT-MORE-DAG: Skipping pass 'Dead Instruction Elimination'
-; OPT-MORE-DAG: Skipping pass 'Lower atomic intrinsics
 
 ; Loop IR passes that opt doesn't turn on by default.
 ; OPT-LOOP-DAG: Skipping pass 'Delete dead loops'
 ; OPT-LOOP-DAG: Skipping pass 'Extract loops into new functions'
 ; OPT-LOOP-DAG: Skipping pass 'Induction Variable Simplification'
 ; OPT-LOOP-DAG: Skipping pass 'Loop Invariant Code Motion'
 ; OPT-LOOP-DAG: Skipping pass 'Loop Strength Reduction'
 ; OPT-LOOP-DAG: Skipping pass 'Recognize loop idioms'
 ; OPT-LOOP-DAG: Skipping pass 'Reroll loops'
 ; OPT-LOOP-DAG: Skipping pass 'Rotate Loops'
 ; OPT-LOOP-DAG: Skipping pass 'Simplify instructions in loops'
 ; OPT-LOOP-DAG: Skipping pass 'Unroll loops'
 ; OPT-LOOP-DAG: Skipping pass 'Unswitch loops'

llvm/trunk/test/Transforms/LowerAtomic/atomic-swap.ll

 ; CHECK-LABEL: @swap(
   %i = alloca i8
   %j = atomicrmw xchg i8* %i, i8 42 monotonic
 ; CHECK: [[INST:%[a-z0-9]+]] = load
 ; CHECK-NEXT: store
   ret i8 %j
 ; CHECK: ret i8 [[INST]]
 }
+
+
+define i8 @swap_optnone() noinline optnone {
+; CHECK-LABEL: @swap_optnone(
+  %i = alloca i8
+  %j = atomicrmw xchg i8* %i, i8 42 monotonic
+; CHECK: [[INST:%[a-z0-9]+]] = load
+; CHECK-NEXT: store
+  ret i8 %j
+; CHECK: ret i8 [[INST]]
+}