[InstCombine] Revert r238452: Fold IntToPtr and PtrToInt into preceding loads.

According to git bisect, this is the root cause of a miscompile for Regex in
libLLVMSupport. I am still working on reducing a test case.
The actual bug may be elsewhere and this commit just exposed it.

Anyway, at the moment, to reproduce, follow these steps:
1. Build clang and libLTO in release mode.
2. Create a new build directory <stage2> and cd into it.
3. Use clang and libLTO from #1 to build llvm-extract in Release mode + asserts
   using -O2 -flto
4. Run llvm-extract  -ralias '.*bar' -S test/Other/extract-alias.ll

Result:
program doesn't contain global named '.*bar'!

Expected result:
@a0a0bar = alias void ()* @bar
@a0bar = alias void ()* @bar

declare void @bar()

Note: In step #3, if you don't use lto or asserts, the miscompile disappears.
llvm-svn: 259674

1 files changed, 5 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 985e2b01a69..9573aab6dcb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -495,17 +495,12 @@ static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
   }
 
   // Fold away bit casts of the loaded value by loading the desired type.
-  // We can do this for BitCastInsts as well as casts from and to pointer types,
-  // as long as those are noops (i.e., the source or dest type have the same
-  // bitwidth as the target's pointers).
   if (LI.hasOneUse())
-    if (auto* CI = dyn_cast<CastInst>(LI.user_back())) {
-      if (CI->isNoopCast(DL)) {
-        LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
-        CI->replaceAllUsesWith(NewLoad);
-        IC.eraseInstFromFunction(*CI);
-        return &LI;
-      }
+    if (auto *BC = dyn_cast<BitCastInst>(LI.user_back())) {
+      LoadInst *NewLoad = combineLoadToNewType(IC, LI, BC->getDestTy());
+      BC->replaceAllUsesWith(NewLoad);
+      IC.eraseInstFromFunction(*BC);
+      return &LI;
     }
 
   // FIXME: We should also canonicalize loads of vectors when their elements are