[AssumeBundles] preserve knowledge in DSE

[jdoerfert]

LGTM.

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/DebugCounter.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <iterator>
 #include <map>
 #include <utility>
 
do {
     // Mark the DeadInst as dead in the list of throwable instructions.
     auto It = ThrowableInst.find(DeadInst);
     if (It != ThrowableInst.end())
       ThrowableInst[It->first] = false;
     ++NumFastOther;
 
     // Try to preserve debug information attached to the dead instruction.
     salvageDebugInfoOrMarkUndef(*DeadInst);
+    salvageKnowledge(DeadInst);
 
     // This instruction is dead, zap it, in stages.  Start by removing it from
     // MemDep, which needs to know the operands and needs it to be in the
     // function.
     MD.removeInstruction(DeadInst);
 
     for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
       Value *Op = DeadInst->getOperand(op);
void deleteDeadInstruction(Instruction *SI) {
     --NumFastOther;
 
     while (!NowDeadInsts.empty()) {
       Instruction *DeadInst = NowDeadInsts.pop_back_val();
       ++NumFastOther;
 
       // Try to preserve debug information attached to the dead instruction.
       salvageDebugInfo(*DeadInst);
+      salvageKnowledge(DeadInst);
 
       // Remove the Instruction from MSSA.
       if (MemoryAccess *MA = MSSA.getMemoryAccess(DeadInst)) {
         if (MemoryDef *MD = dyn_cast<MemoryDef>(MA)) {
           SkipStores.insert(MD);
         }
         Updater.removeMemoryAccess(MA);
       }

llvm/test/Transforms/DeadStoreElimination/MSSA/simple-preservation.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -aa-pipeline=basic-aa -passes=dse -enable-dse-memoryssa -enable-knowledge-retention -S | FileCheck %s
+
+target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
+
+define void @test1(i32* %Q, i32* %P) {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(i32* [[Q:%.*]], i64 4), "nonnull"(i32* [[Q]]) ]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(i32* [[P:%.*]], i64 4), "nonnull"(i32* [[P]]) ]
+; CHECK-NEXT:    store i32 0, i32* [[P]]
+; CHECK-NEXT:    ret void
+;
+  %DEAD = load i32, i32* %Q
+  store i32 %DEAD, i32* %P
+  store i32 0, i32* %P
+  ret void
+}