[SROA] Disable non-whole-alloca splits by default

This patch introduce a switch to control splitting of non-whole-alloca slices with default off.
The switch will be default on again after fixing an issue reported in PR35657.

llvm-svn: 320958

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index 2e5023398f2..bfe3754f076 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -124,6 +124,11 @@ static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
 static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", cl::init(false),
                                         cl::Hidden);
 
+/// Hidden option to allow more aggressive splitting.
+static cl::opt<bool>
+SROASplitNonWholeAllocaSlices("sroa-split-nonwhole-alloca-slices",
+                              cl::init(false), cl::Hidden);
+
 namespace {
 
 /// \brief A custom IRBuilder inserter which prefixes all names, but only in
@@ -4058,7 +4063,7 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
 
   uint64_t AllocaSize = DL.getTypeAllocSize(AI.getAllocatedType());
   const uint64_t MaxBitVectorSize = 1024;
-  if (AllocaSize <= MaxBitVectorSize) {
+  if (SROASplitNonWholeAllocaSlices && AllocaSize <= MaxBitVectorSize) {
     // If a byte boundary is included in any load or store, a slice starting or
     // ending at the boundary is not splittable.
     SmallBitVector SplittableOffset(AllocaSize + 1, true);