[DAGCombiner] [CodeGenPrepare] More comprehensive GEP splitting

Some GEPs were not being split, presumably because that split would just be 
undone by the DAGCombiner. Not performing those splits can prevent important 
optimizations, such as preventing the element indices / member offsets from 
being (partially) folded into load/store instruction immediates. This patch:

- Makes the splits also occur in the cases where the base address and the GEP 
  are in the same BB.
- Ensures that the DAGCombiner doesn't reassociate them back again.

Differential Revision: https://reviews.llvm.org/D60294

llvm-svn: 363544

1 files changed, 4 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index f2df4977f16..52b4bbea012 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -4202,15 +4202,11 @@ bool AddressingModeMatcher::matchOperationAddr(User *AddrInst, unsigned Opcode,
         if (isa<Argument>(Base) || isa<GlobalValue>(Base) ||
             (BaseI && !isa<CastInst>(BaseI) &&
              !isa<GetElementPtrInst>(BaseI))) {
-          // If the base is an instruction, make sure the GEP is not in the same
-          // basic block as the base. If the base is an argument or global
-          // value, make sure the GEP is not in the entry block.  Otherwise,
-          // instruction selection can undo the split.  Also make sure the
-          // parent block allows inserting non-PHI instructions before the
-          // terminator.
+          // Make sure the parent block allows inserting non-PHI instructions
+          // before the terminator.
           BasicBlock *Parent =
               BaseI ? BaseI->getParent() : &GEP->getFunction()->getEntryBlock();
-          if (GEP->getParent() != Parent && !Parent->getTerminator()->isEHPad())
+          if (!Parent->getTerminator()->isEHPad())
             LargeOffsetGEP = std::make_pair(GEP, ConstantOffset);
         }
       }
@@ -4740,8 +4736,7 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
         InsertedInsts, PromotedInsts, TPT, LargeOffsetGEP);
 
     GetElementPtrInst *GEP = LargeOffsetGEP.first;
-    if (GEP && GEP->getParent() != MemoryInst->getParent() &&
-        !NewGEPBases.count(GEP)) {
+    if (GEP && !NewGEPBases.count(GEP)) {
       // If splitting the underlying data structure can reduce the offset of a
       // GEP, collect the GEP.  Skip the GEPs that are the new bases of
       // previously split data structures.