Teach the load analysis driving core instcombine logic and other bits of

logic to look through pointer casts, making them trivially stronger in
the face of loads and stores with intervening pointer casts.

I've included a few test cases that demonstrate the kind of folding
instcombine can do without pointer casts and then variations which
obfuscate the logic through bitcasts. Without this patch, the variations
all fail to optimize fully.

This is more important now than it has been in the past as I've started
moving the load canonicialization to more closely follow the value type
requirements rather than the pointer type requirements and thus this
needs to be prepared for more pointer casts. When I made the same change
to stores several test cases regressed without logic along these lines
so I wanted to systematically improve matters first.

llvm-svn: 220178

2 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 8e13dde0854..32ac62e74c0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -420,7 +420,8 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   // separated by a few arithmetic operations.
   BasicBlock::iterator BBI = &LI;
   if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6))
-    return ReplaceInstUsesWith(LI, AvailableVal);
+    return ReplaceInstUsesWith(
+        LI, Builder->CreateBitCast(AvailableVal, LI.getType()));
 
   // load(gep null, ...) -> unreachable
   if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 924d4e14677..fbb5c201347 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -901,6 +901,9 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
     // If the returned value is the load itself, replace with an undef. This can
     // only happen in dead loops.
     if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
+    if (AvailableVal->getType() != LI->getType())
+      AvailableVal = CastInst::Create(CastInst::BitCast, AvailableVal,
+                                      LI->getType(), "", LI);
     LI->replaceAllUsesWith(AvailableVal);
     LI->eraseFromParent();
     return true;
@@ -1031,7 +1034,13 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
     assert(I != AvailablePreds.end() && I->first == P &&
            "Didn't find entry for predecessor!");
 
-    PN->addIncoming(I->second, I->first);
+    // If we have an available predecessor but it requires casting, insert the
+    // cast in the predecessor and use the cast.
+    Value *PredV = I->second;
+    if (PredV->getType() != LI->getType())
+      PredV = CastInst::Create(CastInst::BitCast, PredV, LI->getType(), "", P);
+
+    PN->addIncoming(PredV, I->first);
   }
 
   //cerr << "PRE: " << *LI << *PN << "\n";