[RS4GC] Revert optimization attempt due to memory corruption

This change reverts "246133 [RewriteStatepointsForGC] Reduce the number of new instructions for base pointers" and a follow on bugfix 12575.

As pointed out in pr25846, this code suffers from a memory corruption bug.  Since I'm (empirically) not going to get back to this any time soon, simply reverting the problematic change is the right answer.

llvm-svn: 261565

6 files changed, 44 insertions, 76 deletions

diff --git a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
index 4c86eeb7350..d2eac9112ea 100644
--- a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -14,7 +14,6 @@
 
 #include "llvm/Pass.h"
 #include "llvm/Analysis/CFG.h"
-#include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/ADT/SetOperations.h"
 #include "llvm/ADT/Statistic.h"
@@ -1025,68 +1024,6 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
 
   }
 
-  // Now that we're done with the algorithm, see if we can optimize the 
-  // results slightly by reducing the number of new instructions needed. 
-  // Arguably, this should be integrated into the algorithm above, but 
-  // doing as a post process step is easier to reason about for the moment.
-  DenseMap<Value *, Value *> ReverseMap;
-  SmallPtrSet<Instruction *, 16> NewInsts;
-  SmallSetVector<AssertingVH<Instruction>, 16> Worklist;
-  // Note: We need to visit the states in a deterministic order.  We uses the
-  // Keys we sorted above for this purpose.  Note that we are papering over a
-  // bigger problem with the algorithm above - it's visit order is not
-  // deterministic.  A larger change is needed to fix this.
-  for (auto Pair : States) {
-    auto *BDV = Pair.first;
-    auto State = Pair.second;
-    Value *Base = State.getBase();
-    assert(BDV && Base);
-    assert(!isKnownBaseResult(BDV) && "why did it get added?");
-    assert(isKnownBaseResult(Base) &&
-           "must be something we 'know' is a base pointer");
-    if (!State.isConflict())
-      continue;
-
-    ReverseMap[Base] = BDV;
-    if (auto *BaseI = dyn_cast<Instruction>(Base)) {
-      NewInsts.insert(BaseI);
-      Worklist.insert(BaseI);
-    }
-  }
-  auto ReplaceBaseInstWith = [&](Value *BDV, Instruction *BaseI,
-                                 Value *Replacement) {
-    // Add users which are new instructions (excluding self references)
-    for (User *U : BaseI->users())
-      if (auto *UI = dyn_cast<Instruction>(U))
-        if (NewInsts.count(UI) && UI != BaseI)
-          Worklist.insert(UI);
-    // Then do the actual replacement
-    NewInsts.erase(BaseI);
-    ReverseMap.erase(BaseI);
-    BaseI->replaceAllUsesWith(Replacement);
-    assert(States.count(BDV));
-    assert(States[BDV].isConflict() && States[BDV].getBase() == BaseI);
-    States[BDV] = BDVState(BDVState::Conflict, Replacement);
-    BaseI->eraseFromParent();
-  };
-  const DataLayout &DL = cast<Instruction>(def)->getModule()->getDataLayout();
-  while (!Worklist.empty()) {
-    Instruction *BaseI = Worklist.pop_back_val();
-    assert(NewInsts.count(BaseI));
-    Value *Bdv = ReverseMap[BaseI];
-    if (auto *BdvI = dyn_cast<Instruction>(Bdv))
-      if (BaseI->isIdenticalTo(BdvI)) {
-        DEBUG(dbgs() << "Identical Base: " << *BaseI << "\n");
-        ReplaceBaseInstWith(Bdv, BaseI, Bdv);
-        continue;
-      }
-    if (Value *V = SimplifyInstruction(BaseI, DL)) {
-      DEBUG(dbgs() << "Base " << *BaseI << " simplified to " << *V << "\n");
-      ReplaceBaseInstWith(Bdv, BaseI, V);
-      continue;
-    }
-  }
-
   // Cache all of our results so we can cheaply reuse them
   // NOTE: This is actually two caches: one of the base defining value
   // relation and one of the base pointer relation!  FIXME
@@ -1094,6 +1031,7 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
     auto *BDV = Pair.first;
     Value *base = Pair.second.getBase();
     assert(BDV && base);
+    assert(!isKnownBaseResult(BDV) && "why did it get added?");
 
     std::string fromstr = cache.count(BDV) ? cache[BDV]->getName() : "none";
     DEBUG(dbgs() << "Updating base value cache"
@@ -1102,6 +1040,8 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
           << " to: " << base->getName() << "\n");
 
     if (cache.count(BDV)) {
+      assert(isKnownBaseResult(base) &&
+             "must be something we 'know' is a base pointer");
       // Once we transition from the BDV relation being store in the cache to
       // the base relation being stored, it must be stable
       assert((!isKnownBaseResult(cache[BDV]) || cache[BDV] == base) &&
diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers-4.ll b/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers-4.ll
index 8d2f8ef921a..5694cfd5ecb 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers-4.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers-4.ll
@@ -1,6 +1,6 @@
 ; RUN: opt < %s -rewrite-statepoints-for-gc -spp-print-base-pointers -S 2>&1 | FileCheck %s
 
-; CHECK: derived %obj_to_consume base %obj_to_consume
+; CHECK: derived %obj_to_consume base %obj_to_consume.base
 
 declare void @foo()
 
diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers.ll b/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers.ll
index 00e71ff88f9..e65897e7a89 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/base-pointers.ll
@@ -81,6 +81,7 @@ entry:
 ; we'd have commoned these, but that's a missed optimization, not correctness.
 ; CHECK-DAG: [ [[DISCARD:%.*.base.relocated.casted]], %loop ]
 ; CHECK-NOT: extra.base
+; CHECK: next.base = select
 ; CHECK: next = select
 ; CHECK: extra2.base = select
 ; CHECK: extra2 = select
@@ -107,7 +108,8 @@ taken:                                            ; preds = %entry
 
 merge:                                            ; preds = %taken, %entry
 ; CHECK-LABEL: merge:
-; CHECK-NEXT: %bdv = phi
+; CHECK-NEXT: phi
+; CHECK-NEXT: phi
 ; CHECK-NEXT: gc.statepoint
   %bdv = phi i64 addrspace(1)* [ %obj, %entry ], [ %obj2, %taken ]
   call void @foo() [ "deopt"(i32 0, i32 -1, i32 0, i32 0, i32 0) ]
@@ -124,7 +126,7 @@ taken:                                            ; preds = %entry
 
 merge:                                            ; preds = %taken, %entry
 ; CHECK-LABEL: merge:
-; CHECK-NEXT: %bdv = phi
+; CHECK-NEXT: phi
 ; CHECK-NEXT: gc.statepoint
   %bdv = phi i64 addrspace(1)* [ %obj, %entry ], [ %obj, %taken ]
   call void @foo() [ "deopt"(i32 0, i32 -1, i32 0, i32 0, i32 0) ]
@@ -138,7 +140,8 @@ entry:
 
 merge:                                            ; preds = %merge, %entry
 ; CHECK-LABEL: merge:
-; CHECK-NEXT: %bdv = phi
+; CHECK-NEXT: phi
+; CHECK-NEXT: phi
 ; CHECK-NEXT: br i1
   %bdv = phi i64 addrspace(1)* [ %obj, %entry ], [ %obj2, %merge ]
   br i1 %cnd, label %merge, label %next
diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/base-vector.ll b/llvm/test/Transforms/RewriteStatepointsForGC/base-vector.ll
index f49d1d9ccdd..2ec82aa2557 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/base-vector.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/base-vector.ll
@@ -45,10 +45,13 @@ untaken2:                                         ; preds = %merge
 
 merge2:                                           ; preds = %untaken2, %taken2
 ; CHECK-LABEL: merge2:
-; CHECK-NEXT: %obj = phi i64 addrspace(1)*
-; CHECK-NEXT: statepoint
+; CHECK: %obj.base = phi i64 addrspace(1)*
+; CHECK: %obj = phi i64 addrspace(1)*
+; CHECK: statepoint
+; CHECK: gc.relocate
+; CHECK-DAG: ; (%obj.base, %obj)
 ; CHECK: gc.relocate
-; CHECK-DAG: ; (%obj, %obj)
+; CHECK-DAG: ; (%obj.base, %obj.base)
   %obj = phi i64 addrspace(1)* [ %obj0, %taken2 ], [ %obj1, %untaken2 ]
   call void @do_safepoint() [ "deopt"() ]
   ret i64 addrspace(1)* %obj
@@ -60,7 +63,7 @@ define i64 addrspace(1)* @test3(i64 addrspace(1)* %ptr) gc "statepoint-example"
 ; CHECK: extractelement
 ; CHECK: statepoint
 ; CHECK: gc.relocate
-; CHECK-DAG: (%obj, %obj)
+; CHECK-DAG: (%obj.base, %obj)
 entry:
   %vec = insertelement <2 x i64 addrspace(1)*> undef, i64 addrspace(1)* %ptr, i32 0
   %obj = extractelement <2 x i64 addrspace(1)*> %vec, i32 0
@@ -72,9 +75,7 @@ define i64 addrspace(1)* @test4(i64 addrspace(1)* %ptr) gc "statepoint-example"
 ; CHECK-LABEL: test4
 ; CHECK: statepoint
 ; CHECK: gc.relocate
-; CHECK-DAG: ; (%ptr, %obj)
-; CHECK: gc.relocate
-; CHECK-DAG: ; (%ptr, %ptr)
+; CHECK-DAG: ; (%obj.base, %obj)
 ; When we can optimize an extractelement from a known
 ; index and avoid introducing new base pointer instructions
 entry:
@@ -91,7 +92,7 @@ declare void @use(i64 addrspace(1)*) "gc-leaf-function"
 define void @test5(i1 %cnd, i64 addrspace(1)* %obj) gc "statepoint-example" {
 ; CHECK-LABEL: @test5
 ; CHECK: gc.relocate
-; CHECK-DAG: (%obj, %bdv)
+; CHECK-DAG: (%bdv.base, %bdv)
 ; When we fundementally have to duplicate
 entry:
   %gep = getelementptr i64, i64 addrspace(1)* %obj, i64 1
diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/live-vector-nosplit.ll b/llvm/test/Transforms/RewriteStatepointsForGC/live-vector-nosplit.ll
index 9b649f2bc68..d3e25d56b6d 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/live-vector-nosplit.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/live-vector-nosplit.ll
@@ -73,9 +73,12 @@ exceptional_return:                               ; preds = %entry
 define <2 x i64 addrspace(1)*> @test5(i64 addrspace(1)* %p) gc "statepoint-example" {
 ; CHECK-LABEL: test5
 ; CHECK: insertelement
+; CHECK-NEXT: insertelement
 ; CHECK-NEXT: gc.statepoint
 ; CHECK-NEXT: gc.relocate
 ; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
 ; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %vec.relocated.casted
 entry:
   %vec = insertelement <2 x i64 addrspace(1)*> undef, i64 addrspace(1)* %p, i32 0
@@ -100,9 +103,12 @@ untaken:                                          ; preds = %entry
 merge:                                            ; preds = %untaken, %taken
 ; CHECK-LABEL: merge:
 ; CHECK-NEXT: = phi
+; CHECK-NEXT: = phi
 ; CHECK-NEXT: gc.statepoint
 ; CHECK-NEXT: gc.relocate
 ; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
 ; CHECK-NEXT: ret <2 x i64 addrspace(1)*>
   %obj = phi <2 x i64 addrspace(1)*> [ %obja, %taken ], [ %objb, %untaken ]
   call void @do_safepoint() [ "deopt"() ]
diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/live-vector.ll b/llvm/test/Transforms/RewriteStatepointsForGC/live-vector.ll
index ab84cbc5e52..a289d47ec81 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/live-vector.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/live-vector.ll
@@ -98,6 +98,9 @@ exceptional_return:                               ; preds = %entry
 define <2 x i64 addrspace(1)*> @test5(i64 addrspace(1)* %p) gc "statepoint-example" {
 ; CHECK-LABEL: test5
 ; CHECK: insertelement
+; CHECK-NEXT: insertelement
+; CHECK-NEXT: extractelement
+; CHECK-NEXT: extractelement
 ; CHECK-NEXT: extractelement
 ; CHECK-NEXT: extractelement
 ; CHECK-NEXT: gc.statepoint
@@ -105,9 +108,15 @@ define <2 x i64 addrspace(1)*> @test5(i64 addrspace(1)* %p) gc "statepoint-examp
 ; CHECK-NEXT: bitcast
 ; CHECK-NEXT: gc.relocate
 ; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
 ; CHECK-NEXT: insertelement
 ; CHECK-NEXT: insertelement
-; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %7
+; CHECK-NEXT: insertelement
+; CHECK-NEXT: insertelement
+; CHECK-NEXT: ret <2 x i64 addrspace(1)*>
 ; A base vector from a load
 entry:
   %vec = insertelement <2 x i64 addrspace(1)*> undef, i64 addrspace(1)* %p, i32 0
@@ -131,6 +140,9 @@ untaken:                                          ; preds = %entry
 merge:                                            ; preds = %untaken, %taken
 ; CHECK-LABEL: merge:
 ; CHECK-NEXT: = phi
+; CHECK-NEXT: = phi
+; CHECK-NEXT: extractelement
+; CHECK-NEXT: extractelement
 ; CHECK-NEXT: extractelement
 ; CHECK-NEXT: extractelement
 ; CHECK-NEXT: gc.statepoint
@@ -138,6 +150,12 @@ merge:                                            ; preds = %untaken, %taken
 ; CHECK-NEXT: bitcast
 ; CHECK-NEXT: gc.relocate
 ; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
+; CHECK-NEXT: gc.relocate
+; CHECK-NEXT: bitcast
+; CHECK-NEXT: insertelement
+; CHECK-NEXT: insertelement
 ; CHECK-NEXT: insertelement
 ; CHECK-NEXT: insertelement
 ; CHECK-NEXT: ret <2 x i64 addrspace(1)*>