SLPVectorizer: Fix stale for Value pointer array

We are slicing an array of Value pointers and process those slices in a loop.
The problem is that we might invalidate a later slice by vectorizing a former
slice.

Use a WeakVH to track the pointer. If the pointer is deleted or RAUW'ed we can
tell.

The test case will only fail when running with libgmalloc.

radar://15498655

llvm-svn: 195162

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -1833,6 +1833,21 @@ private:
   StoreListMap StoreRefs;
 };
 
+/// \brief Check that the Values in the slice in VL array are still existant in
+/// the WeakVH array.
+/// Vectorization of part of the VL array may cause later values in the VL array
+/// to become invalid. We track when this has happened in the WeakVH array.
+static bool hasValueBeenRAUWed(ArrayRef<Value *> &VL,
+                               SmallVectorImpl<WeakVH> &VH,
+                               unsigned SliceBegin,
+                               unsigned SliceSize) {
+  for (unsigned i = SliceBegin; i < SliceBegin + SliceSize; ++i)
+    if (VH[i] != VL[i])
+      return true;
+
+  return false;
+}
+
 bool SLPVectorizer::vectorizeStoreChain(ArrayRef<Value *> Chain,
                                           int CostThreshold, BoUpSLP &R) {
   unsigned ChainLen = Chain.size();
@@ -1845,11 +1860,19 @@ bool SLPVectorizer::vectorizeStoreChain(ArrayRef<Value *> Chain,
   if (!isPowerOf2_32(Sz) || VF < 2)
     return false;
 
+  // Keep track of values that were delete by vectorizing in the loop below.
+  SmallVector<WeakVH, 8> TrackValues(Chain.begin(), Chain.end());
+
   bool Changed = false;
   // Look for profitable vectorizable trees at all offsets, starting at zero.
   for (unsigned i = 0, e = ChainLen; i < e; ++i) {
     if (i + VF > e)
       break;
+
+    // Check that a previous iteration of this loop did not delete the Value.
+    if (hasValueBeenRAUWed(Chain, TrackValues, i, VF))
+      continue;
+
     DEBUG(dbgs() << "SLP: Analyzing " << VF << " stores at offset " << i
           << "\n");
     ArrayRef<Value *> Operands = Chain.slice(i, VF);
@@ -1990,6 +2013,9 @@ bool SLPVectorizer::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R) {
 
   bool Changed = false;
 
+  // Keep track of values that were delete by vectorizing in the loop below.
+  SmallVector<WeakVH, 8> TrackValues(VL.begin(), VL.end());
+
   for (unsigned i = 0, e = VL.size(); i < e; ++i) {
     unsigned OpsWidth = 0;
 
@@ -2001,6 +2027,10 @@ bool SLPVectorizer::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R) {
     if (!isPowerOf2_32(OpsWidth) || OpsWidth < 2)
       break;
 
+    // Check that a previous iteration of this loop did not delete the Value.
+    if (hasValueBeenRAUWed(VL, TrackValues, i, OpsWidth))
+      continue;
+
     DEBUG(dbgs() << "SLP: Analyzing " << OpsWidth << " operations "
                  << "\n");
     ArrayRef<Value *> Ops = VL.slice(i, OpsWidth);

llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll

@@ -0,0 +1,33 @@
+; RUN: opt -slp-vectorizer -S %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n32:64-S128"
+target triple = "x86_64-apple-macosx"
+
+; This test used to fail under libgmalloc. Because we would try to access a
+; pointer that was already deleted.
+;
+; llvm-lit -v --param use_gmalloc=1 --param
+;   gmalloc_path=/usr/lib/libgmalloc.dylib
+;   test/Transforms/LoopVectorize/X86/rauw-bug.ll
+;
+; radar://15498655
+
+; CHECK: reduced
+define void @reduced()  {
+entry:
+  br i1 undef, label %while.body, label %while.cond63.preheader.while.end76_crit_edge
+
+while.cond63.preheader.while.end76_crit_edge:
+  ret void
+
+while.body:
+  %d2_fx.015 = phi double [ %sub52, %while.body ], [ undef, %entry ]
+  %d2_fy.014 = phi double [ %sub58, %while.body ], [ undef, %entry ]
+  %d3_fy.013 = phi double [ %div56, %while.body ], [ undef, %entry ]
+  %d3_fx.012 = phi double [ %div50, %while.body ], [ undef, %entry ]
+  %div50 = fmul double %d3_fx.012, 1.250000e-01
+  %sub52 = fsub double 0.000000e+00, %div50
+  %div56 = fmul double %d3_fy.013, 1.250000e-01
+  %sub58 = fsub double 0.000000e+00, %div56
+  br label %while.body
+}