[PATCH] D14364: Fix LoopAccessAnalysis when potentially nullptr check are involved

[Mehdi AMINI via llvm-commits]

joker.eph created this revision.
joker.eph added a reviewer: anemet.
joker.eph added subscribers: dexonsmith, llvm-commits.

GetUnderlyingObjects() can return "null" among its list of objects,
we don't want to deduce that two pointers can point to the same
memory in this case, so filter it out.

http://reviews.llvm.org/D14364

Files:
  lib/Analysis/LoopAccessAnalysis.cpp
  test/Analysis/LoopAccessAnalysis/nullptr.ll

Index: test/Analysis/LoopAccessAnalysis/nullptr.ll
===================================================================
--- /dev/null
+++ test/Analysis/LoopAccessAnalysis/nullptr.ll
@@ -0,0 +1,31 @@
+;RUN: opt -loop-accesses -analyze %s  | FileCheck %s
+; CHECK: Memory dependences are safe with run-time checks
+
+; ModuleID = 'bugpoint-reduced-simplified.bc'
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+; Function Attrs: ssp uwtable
+define void @foo(i1 %cond, i32* %ptr1, i32* %ptr2)  {
+  br i1 %cond, label %.preheader, label %diamond
+
+diamond:  ; preds = %.noexc.i.i
+  br label %.preheader
+
+.preheader:                                     ; preds = %diamond, %0
+  %ptr1_or_null = phi i32* [ null, %0 ], [ %ptr1, %diamond ]
+  %ptr2_or_null = phi i32* [ null, %0 ], [ %ptr2, %diamond ]
+  br label %.lr.ph
+
+.lr.ph:                                           ; preds = %.lr.ph, %.preheader
+  %indvars.iv = phi i64 [ %indvars.iv.next, %.lr.ph ], [ 10, %.preheader ]
+  %indvars.iv.next = add nsw i64 %indvars.iv, -1
+  %tmp4 = getelementptr inbounds i32, i32* %ptr2_or_null, i64 %indvars.iv.next
+  %tmp5 = load i32, i32* %tmp4, align 4
+  %tmp6 = getelementptr inbounds i32, i32* %ptr1_or_null, i64 %indvars.iv.next
+  store i32 undef, i32* %tmp6, align 4
+  br i1 false, label %.lr.ph, label %.end
+
+.end:
+  ret void
+}
Index: lib/Analysis/LoopAccessAnalysis.cpp
===================================================================
--- lib/Analysis/LoopAccessAnalysis.cpp
+++ lib/Analysis/LoopAccessAnalysis.cpp
@@ -743,6 +743,11 @@
           GetUnderlyingObjects(Ptr, TempObjects, DL, LI);
           DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n");
           for (Value *UnderlyingObj : TempObjects) {
+            // nullptr never alias, don't join sets for pointer that have "null"
+            // in their UnderlyingObjects list.
+            if (isa<ConstantPointerNull>(UnderlyingObj)) {
+              continue;
+            }
             UnderlyingObjToAccessMap::iterator Prev =
                 ObjToLastAccess.find(UnderlyingObj);
             if (Prev != ObjToLastAccess.end())


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