[LICM] Clear LoopToAliasSetMap when a loop being deleted is outermost or removed from its parent loop.

[huihuiz]

Summary

Fix pr31141.

If a loop is nested inside another loop, alias information is saved in
LoopToAliasSetMap. Later when processing the outer loop, this alias
information is collected and erased from LoopToAliasSetMap.

However, when the outer loop is deleted by other loop pass, the information
saved in LoopToAliasSetMap by its subloops will not get erased. This patch
clear the LoopToAliasSetMap when a loop being deleted is outermost or
removed from its parent loop.

[efriedma]

The commit message should refer to https://bugs.llvm.org/show_bug.cgi?id=31141 (assuming this patch fixes that bug).

lib/Transforms/Scalar/LICM.cpp

1600

Need an explanation here for why we're clearing the map in exactly these circumstances. It isn't obvious that we won't lose useful cached information, or that we don't need to clear the map if the loop has a parent.

[huihuiz]

Patch will fix pr31141
https://bugs.llvm.org/show_bug.cgi?id=31141

[huihuiz]

Clear the LoopToAliasSetMap only when the loop being deleted is outermost loop
or removed from its parent. Otherwise, the alias information saved by its subloops
is cached, and later collected and erased by their nearest outer loop.

[huihuiz]

Update comment message.

lib/Transforms/Scalar/LICM.cpp

     return;
 
   ASTIt->second->deleteValue(V);
 }
 
 /// Simple Analysis hook. Delete value L from alias set map.
 ///
 void LegacyLICMPass::deleteAnalysisLoop(Loop *L) {
+  // If the loop being deleted is outermost, or removed from its parent loop,
+  // then the alias information saved by its subloops need to be cleared.
+  // Otherwise, the alias information is cached, later collected and erased
+  // by the nearest outer loop.
+  if (!L->getParentLoop())
+    LICM.getLoopToAliasSetMap().clear();
+
   if (!LICM.getLoopToAliasSetMap().count(L))
     return;
 
   LICM.getLoopToAliasSetMap().erase(L);
 }
 
 static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                      AliasSetTracker *CurAST, Loop *CurLoop,

test/Transforms/LICM/outer-loop-fully-unrolled.ll

+; RUN: opt -S -loop-unroll -licm < %s | FileCheck %s
+
+; Check that when the outer most loop is fully unrolled, the alias information
+; saved in the LoopToAliasSetMap is cleared, without triggering an assertion in
+; doFinalizaton().
+
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+; CHECK: store double %{{.+}}, double* %{{.+}}
+
+define void @foo(double** %A) {
+entry:
+  br label %for.cond1.preheader
+
+for.cond1.preheader:
+  %i = phi i32 [ 1, %entry ], [ %inc.i, %for.cond.cleanup3 ]
+  %arrayidx1 = getelementptr inbounds double*, double** %A, i32 %i
+  %t0 = load double*, double** %arrayidx1, align 4
+  br label %for.body4
+
+for.cond.cleanup:
+  ret void
+
+for.cond.cleanup3:
+  %inc.i = add nuw nsw i32 %i, 1
+  %exitcond = icmp eq i32 %inc.i, 9
+  br i1 %exitcond, label %for.cond.cleanup, label %for.cond1.preheader
+
+for.body4:
+  %j = phi i32 [ 0, %for.cond1.preheader ], [ %inc.j, %for.body4 ]
+  %arrayidx2 = getelementptr inbounds double*, double** %A, i32 %j
+  %t1 = load double*, double** %arrayidx2, align 4
+  %arrayidx3 = getelementptr inbounds double, double* %t1, i32 %i
+  %t2 = load double, double* %arrayidx3, align 8
+  %arrayidx4 = getelementptr inbounds double, double* %t0, i32 %j
+  store double %t2, double* %arrayidx4, align 8
+  %inc.j = add nuw nsw i32 %j, 1
+  %cmp2 = icmp eq i32 %inc.j, %i
+  br i1 %cmp2, label %for.cond.cleanup3, label %for.body4
+}
+