[LICM] Allow AliasSetMap to contain top-level loops.

[fhahn]

Summary

When an outer loop gets deleted by a different pass, before LICM visits
it, we cannot clean up its sub-loops in AliasSetMap, because at the
point we receive the deleteAnalysisLoop callback for the outer loop, the loop
object is already invalid and we cannot access its sub-loops any longer.

[asbirlea]

Thank you for this! This LGTM.
The caching of AliasSetTracker objects will go away when MemorySSA is enabled.

[fhahn]

Thanks!

[uabelho]

Hi,

@fhahn : I noticed that https://bugs.llvm.org/show_bug.cgi?id=31141 stopped crashing with this patch, do you think it's by accident or can that possibly be closed now?

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

void getAnalysisUsage(AnalysisUsage &AU) const override {
     }
     AU.addRequired<TargetTransformInfoWrapperPass>();
     getLoopAnalysisUsage(AU);
   }
 
   using llvm::Pass::doFinalization;
 
   bool doFinalization() override {
-    assert(LICM.getLoopToAliasSetMap().empty() &&
+    auto &AliasSetMap = LICM.getLoopToAliasSetMap();
+    // All loops in the AliasSetMap should be cleaned up already. The only case
+    // where we fail to do so is if an outer loop gets deleted before LICM
+    // visits it.
+    assert(all_of(AliasSetMap,
+                  [](LoopInvariantCodeMotion::ASTrackerMapTy::value_type &KV) {
+                    return !KV.first->getParentLoop();
+                  }) &&
            "Didn't free loop alias sets");
+    AliasSetMap.clear();
     return false;
   }
 
 private:
   LoopInvariantCodeMotion LICM;
 
   /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
   void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,

llvm/trunk/test/Transforms/LICM/outer-loop-deleted-before-licm.ll

+; RUN: opt %s -S -loop-unroll -licm | FileCheck %s
+
+; Check that we can deal with loops where a parent loop gets deleted before it
+; is visited by LICM.
+define void @test() {
+; CHECK-LABEL: define void @test() {
+; CHECK-LABEL: entry:
+; CHECK-NEXT:    br label %for.body43
+
+; CHECK-LABEL: for.body43:                                       ; preds = %entry
+; CHECK-NEXT:    br label %if.else75
+
+; CHECK-LABEL: if.else75:                                        ; preds = %for.body43
+; CHECK-NEXT:    br label %for.body467
+
+; CHECK-LABEL: for.body467:                                      ; preds = %for.body467.for.body467_crit_edge, %if.else75
+; CHECK-NEXT:    br label %for.body467.for.body467_crit_edge
+
+; CHECK-LABEL: for.body467.for.body467_crit_edge:                ; preds = %for.body467
+; CHECK-NEXT:    br i1 false, label %for.end539, label %for.body467
+
+; CHECK-LABEL: for.end539:                                       ; preds = %for.body467.for.body467_crit_edge
+; CHECK-NEXT:    ret void
+;
+
+entry:
+  br label %for.body43
+
+for.body43:                                       ; preds = %for.end539, %entry
+  br label %if.else75
+
+if.else75:                                        ; preds = %for.body43
+  br label %for.body467
+
+for.body467:                                      ; preds = %for.body467.for.body467_crit_edge, %if.else75
+  br label %for.body467.for.body467_crit_edge
+
+for.body467.for.body467_crit_edge:                ; preds = %for.body467
+  br i1 false, label %for.end539, label %for.body467
+
+for.end539:                                       ; preds = %for.body467
+  br i1 undef, label %for.body43, label %for.end547
+
+for.end547:                                       ; preds = %for.body43
+  ret void
+}