Remove align assumptions if possible.

Author: fhahn

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -3226,6 +3226,42 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         MaybeSimplifyHint(OBU.Inputs[0]);
         MaybeSimplifyHint(OBU.Inputs[1]);
       }
+
+      if (OBU.getTagName() == "align" && OBU.Inputs.size() == 2) {
+        RetainedKnowledge RK = getKnowledgeFromBundle(
+            *cast<AssumeInst>(II), II->bundle_op_info_begin()[Idx]);
+        if (!RK || RK.AttrKind != Attribute::Alignment ||
+            !isPowerOf2_64(RK.ArgValue))
+          continue;
+        SetVector<const Instruction *> WorkList;
+        bool AlignNeeded = false;
+        WorkList.insert(II);
+        for (unsigned I = 0; I != WorkList.size(); ++I) {
+          if (auto *LI = dyn_cast<LoadInst>(WorkList[I])) {
+            if (auto *AlignMD = LI->getMetadata(LLVMContext::MD_align)) {
+              auto *A = mdconst::extract<ConstantInt>(AlignMD->getOperand(0));
+
+              if (A->getZExtValue() % RK.ArgValue != 0) {
+                AlignNeeded = true;
+                break;
+              }
+            }
+          }
+          if (isa<ICmpInst>(WorkList[I])) {
+            AlignNeeded = true;
+            break;
+          }
+          if (WorkList.size() > 16) {
+            AlignNeeded = true;
+            break;
+          }
+
+          for (const User *U : WorkList[I]->users())
+            WorkList.insert(cast<Instruction>(U));
+        }
+        auto *New = CallBase::removeOperandBundle(II, OBU.getTagID());
+        return New;
+      }
     }
 
     // Convert nonnull assume like: