Refine the set of UniformAfterVectorization instructions.

Except the seed uniform instructions (conditional branch and consecutive ptr
instructions), dependencies to be added into uniform set should only be used
by existing uniform instructions or intructions outside of current loop.

Differential Revision: http://reviews.llvm.org/D21755


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274262 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -5007,38 +5007,83 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
 void LoopVectorizationLegality::collectLoopUniforms() {
   // We now know that the loop is vectorizable!
   // Collect variables that will remain uniform after vectorization.
-  std::vector<Value *> Worklist;
-  BasicBlock *Latch = TheLoop->getLoopLatch();
 
-  // Start with the conditional branch and walk up the block.
-  Worklist.push_back(Latch->getTerminator()->getOperand(0));
+  // If V is not an instruction inside the current loop, it is a Value
+  // outside of the scope which we are interesting in.
+  auto isOutOfScope = [&](Value *V) -> bool {
+    Instruction *I = dyn_cast<Instruction>(V);
+    return (!I || !TheLoop->contains(I));
+  };
+
+  SetVector<Instruction *> Worklist;
+  BasicBlock *Latch = TheLoop->getLoopLatch();
+  // Start with the conditional branch.
+  if (!isOutOfScope(Latch->getTerminator()->getOperand(0))) {
+    Instruction *Cmp = cast<Instruction>(Latch->getTerminator()->getOperand(0));
+    Worklist.insert(Cmp);
+    DEBUG(dbgs() << "LV: Found uniform instruction: " << *Cmp << "\n");
+  }
 
   // Also add all consecutive pointer values; these values will be uniform
-  // after vectorization (and subsequent cleanup) and, until revectorization is
-  // supported, all dependencies must also be uniform.
-  for (Loop::block_iterator B = TheLoop->block_begin(),
-                            BE = TheLoop->block_end();
-       B != BE; ++B)
-    for (Instruction &I : **B)
-      if (I.getType()->isPointerTy() && isConsecutivePtr(&I))
-        Worklist.insert(Worklist.end(), I.op_begin(), I.op_end());
-
-  while (!Worklist.empty()) {
-    Instruction *I = dyn_cast<Instruction>(Worklist.back());
-    Worklist.pop_back();
-
-    // Look at instructions inside this loop.
-    // Stop when reaching PHI nodes.
-    // TODO: we need to follow values all over the loop, not only in this block.
-    if (!I || !TheLoop->contains(I) || isa<PHINode>(I))
-      continue;
-
-    // This is a known uniform.
-    Uniforms.insert(I);
-
-    // Insert all operands.
-    Worklist.insert(Worklist.end(), I->op_begin(), I->op_end());
+  // after vectorization (and subsequent cleanup).
+  for (auto *BB : TheLoop->getBlocks()) {
+    for (auto &I : *BB) {
+      if (I.getType()->isPointerTy() && isConsecutivePtr(&I)) {
+        Worklist.insert(&I);
+        DEBUG(dbgs() << "LV: Found uniform instruction: " << I << "\n");
+      }
+    }
   }
+
+  // Expand Worklist in topological order: whenever a new instruction
+  // is added , its users should be either already inside Worklist, or
+  // out of scope. It ensures a uniform instruction will only be used
+  // by uniform instructions or out of scope instructions.
+  unsigned idx = 0;
+  do {
+    Instruction *I = Worklist[idx++];
+
+    for (auto OV : I->operand_values()) {
+      if (isOutOfScope(OV))
+        continue;
+      Instruction *OI = cast<Instruction>(OV);
+      if (std::all_of(OI->user_begin(), OI->user_end(), [&](User *U) -> bool {
+            return isOutOfScope(U) || Worklist.count(cast<Instruction>(U));
+          })) {
+        Worklist.insert(OI);
+        DEBUG(dbgs() << "LV: Found uniform instruction: " << *OI << "\n");
+      }
+    }
+  } while (idx != Worklist.size());
+
+  // For an instruction to be added into Worklist above, all its users inside
+  // the current loop should be already added into Worklist. This condition
+  // cannot be true for phi instructions which is always in a dependence loop.
+  // Because any instruction in the dependence cycle always depends on others
+  // in the cycle to be added into Worklist first, the result is no ones in
+  // the cycle will be added into Worklist in the end.
+  // That is why we process PHI separately.
+  for (auto &Induction : *getInductionVars()) {
+    auto *PN = Induction.first;
+    auto *UpdateV = PN->getIncomingValueForBlock(TheLoop->getLoopLatch());
+    if (std::all_of(PN->user_begin(), PN->user_end(),
+                    [&](User *U) -> bool {
+                      return U == UpdateV || isOutOfScope(U) ||
+                             Worklist.count(cast<Instruction>(U));
+                    }) &&
+        std::all_of(UpdateV->user_begin(), UpdateV->user_end(),
+                    [&](User *U) -> bool {
+                      return U == PN || isOutOfScope(U) ||
+                             Worklist.count(cast<Instruction>(U));
+                    })) {
+      Worklist.insert(cast<Instruction>(PN));
+      Worklist.insert(cast<Instruction>(UpdateV));
+      DEBUG(dbgs() << "LV: Found uniform instruction: " << *PN << "\n");
+      DEBUG(dbgs() << "LV: Found uniform instruction: " << *UpdateV << "\n");
+    }
+  }
+
+  Uniforms.insert(Worklist.begin(), Worklist.end());
 }
 
 bool LoopVectorizationLegality::canVectorizeMemory() {

test/Transforms/LoopVectorize/X86/uniform-phi.ll

@@ -0,0 +1,50 @@
+; RUN: opt < %s  -loop-vectorize -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7 -debug-only=loop-vectorize -S 2>&1 | FileCheck %s
+; REQUIRES: asserts
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK-LABEL: test
+; CHECK-DAG: LV: Found uniform instruction:   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+; CHECK-DAG: LV: Found uniform instruction:   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+; CHECK-DAG: LV: Found uniform instruction:   %exitcond = icmp eq i64 %indvars.iv, 1599
+
+define void @test(float* noalias nocapture %a, float* noalias nocapture readonly %b) #0 {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %b, i64 %indvars.iv
+  %tmp0 = load float, float* %arrayidx, align 4
+  %add = fadd float %tmp0, 1.000000e+00
+  %arrayidx5 = getelementptr inbounds float, float* %a, i64 %indvars.iv
+  store float %add, float* %arrayidx5, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv, 1599
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+; CHECK-LABEL: foo
+; CHECK-DAG: LV: Found uniform instruction:   %cond = icmp eq i64 %i.next, %n
+; CHECK-DAG: LV: Found uniform instruction:   %tmp1 = getelementptr inbounds i32, i32* %a, i32 %tmp0
+; CHECK-NOT: LV: Found uniform instruction:   %i = phi i64 [ %i.next, %for.body ], [ 0, %entry ]
+
+define void @foo(i32* %a, i64 %n) {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [ %i.next, %for.body ], [ 0, %entry ]
+  %tmp0 = trunc i64 %i to i32
+  %tmp1 = getelementptr inbounds i32, i32* %a, i32 %tmp0
+  store i32 %tmp0, i32* %tmp1, align 4
+  %i.next = add nuw nsw i64 %i, 1
+  %cond = icmp eq i64 %i.next, %n
+  br i1 %cond, label %for.end, label %for.body
+
+for.end:
+  ret void
+}