[llvm] r274237 - [DSE] Fix bug in partial overwrite tracking

[Jun Bum Lim via llvm-commits]

Author: junbuml
Date: Thu Jun 30 10:32:20 2016
New Revision: 274237

URL: http://llvm.org/viewvc/llvm-project?rev=274237&view=rev
Log:
[DSE] Fix bug in partial overwrite tracking

Summary:
Found cases where DSE incorrectly add partially-overwritten intervals.
Please see the test case for details.

Reviewers: mcrosier, eeckstein, hfinkel

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D21859

Modified:
    llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/trunk/test/Transforms/DeadStoreElimination/combined-partial-overwrites.ll

Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=274237&r1=274236&r2=274237&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Thu Jun 30 10:32:20 2016
@@ -385,18 +385,25 @@ static OverwriteResult isOverwrite(const
     // Find any intervals ending at, or after, LaterIntStart which start
     // before LaterIntEnd.
     auto ILI = IM.lower_bound(LaterIntStart);
-    if (ILI != IM.end() && ILI->second < LaterIntEnd) {
-      // This existing interval ends in the middle of
-      // [LaterIntStart, LaterIntEnd), erase it adjusting our start.
+    if (ILI != IM.end() && ILI->second <= LaterIntEnd) {
+      // This existing interval is overlapped with the current store somewhere
+      // in [LaterIntStart, LaterIntEnd]. Merge them by erasing the existing
+      // intervals and adjusting our start and end.
       LaterIntStart = std::min(LaterIntStart, ILI->second);
       LaterIntEnd = std::max(LaterIntEnd, ILI->first);
       ILI = IM.erase(ILI);
 
-      while (ILI != IM.end() && ILI->first <= LaterIntEnd)
-        ILI = IM.erase(ILI);
-
-      if (ILI != IM.end() && ILI->second < LaterIntEnd)
+      // Continue erasing and adjusting our end in case other previous
+      // intervals are also overlapped with the current store.
+      //
+      // |--- ealier 1 ---|  |--- ealier 2 ---|
+      //     |------- later---------|
+      //
+      while (ILI != IM.end() && ILI->second <= LaterIntEnd) {
+        assert(ILI->second > LaterIntStart && "Unexpected interval");
         LaterIntEnd = std::max(LaterIntEnd, ILI->first);
+        ILI = IM.erase(ILI);
+      }
     }
 
     IM[LaterIntEnd] = LaterIntStart;

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/combined-partial-overwrites.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/combined-partial-overwrites.ll?rev=274237&r1=274236&r2=274237&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/combined-partial-overwrites.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/combined-partial-overwrites.ll Thu Jun 30 10:32:20 2016
@@ -198,3 +198,42 @@ entry:
   ret i8 0
 }
 
+define signext i8 @test6(i32 *%ptr) {
+entry:
+; CHECK-LABEL: @test6
+
+  store i32 0, i32* %ptr
+
+  %bptr = bitcast i32* %ptr to i16*
+  %bptr1 = getelementptr inbounds i16, i16* %bptr, i64 0
+  %bptr2 = getelementptr inbounds i16, i16* %bptr, i64 1
+
+  store i16 1456, i16* %bptr2, align 1
+  store i16 65535, i16* %bptr1, align 1
+
+; CHECK-NOT: store i32 0, i32* %ptr
+
+  ret i8 0
+}
+
+define signext i8 @test7(i64 *%ptr) {
+entry:
+; CHECK-LABEL: @test7
+
+  store i64 0, i64* %ptr
+
+  %bptr = bitcast i64* %ptr to i16*
+  %bptr1 = getelementptr inbounds i16, i16* %bptr, i64 0
+  %bptr2 = getelementptr inbounds i16, i16* %bptr, i64 1
+  %bptr3 = getelementptr inbounds i16, i16* %bptr, i64 2
+  %bptr4 = getelementptr inbounds i16, i16* %bptr, i64 3
+
+  store i16 1346, i16* %bptr1, align 1
+  store i16 1756, i16* %bptr3, align 1
+  store i16 1456, i16* %bptr2, align 1
+  store i16 5656, i16* %bptr4, align 1
+
+; CHECK-NOT: store i64 0, i64* %ptr
+
+  ret i8 0
+}