Revert rL319407: [SROA] enable splitting for non-whole-alloca loads and stores

This reverts commit rL319407 due to failures in some buildbot.

llvm-svn: 319410

1 files changed, 10 insertions, 21 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index d0431d48a43..bd064978b64 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -30,7 +30,6 @@
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
@@ -4048,31 +4047,21 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
   // First try to pre-split loads and stores.
   Changed |= presplitLoadsAndStores(AI, AS);
 
-  // Now that we have identified any pre-splitting opportunities,
-  // mark loads and stores unsplittable except for the following case.
-  // We leave a slice splittable if all other slices are disjoint or fully
-  // included in the slice, such as whole-alloca loads and stores.
-  // If we fail to split these during pre-splitting, we want to force them
-  // to be rewritten into a partition.
+  // Now that we have identified any pre-splitting opportunities, mark any
+  // splittable (non-whole-alloca) loads and stores as unsplittable. If we fail
+  // to split these during pre-splitting, we want to force them to be
+  // rewritten into a partition.
   bool IsSorted = true;
-
-  // If a byte boundary is included in any load or store, a slice starting or
-  // ending at the boundary is not splittable.
-  unsigned AllocaSize = DL.getTypeAllocSize(AI.getAllocatedType());
-  SmallBitVector SplittableOffset(AllocaSize+1, true);
-  for (Slice &S : AS)
-    for (unsigned O = S.beginOffset() + 1; O < S.endOffset() && O < AllocaSize;
-         O++)
-      SplittableOffset.reset(O);
-
   for (Slice &S : AS) {
     if (!S.isSplittable())
       continue;
-
-    if ((S.beginOffset() > AllocaSize || SplittableOffset[S.beginOffset()]) &&
-        (S.endOffset() > AllocaSize || SplittableOffset[S.endOffset()]))
+    // FIXME: We currently leave whole-alloca splittable loads and stores. This
+    // used to be the only splittable loads and stores and we need to be
+    // confident that the above handling of splittable loads and stores is
+    // completely sufficient before we forcibly disable the remaining handling.
+    if (S.beginOffset() == 0 &&
+        S.endOffset() >= DL.getTypeAllocSize(AI.getAllocatedType()))
       continue;
-
     if (isa<LoadInst>(S.getUse()->getUser()) ||
         isa<StoreInst>(S.getUse()->getUser())) {
       S.makeUnsplittable();