[CGP] Ensure sinking multiple instructions does not invalidate dominance checks

In MVE, as of rL371218, we are attempting to sink chains of instructions such as:
  %l1 = insertelement <8 x i8> undef, i8 %l0, i32 0
  %broadcast.splat26 = shufflevector <8 x i8> %l1, <8 x i8> undef, <8 x i32> zeroinitializer
In certain situations though, we can end up breaking the dominance relations of
instructions. This happens when we sink the instruction into a loop, but cannot
remove the originals. The Use is updated, which might in fact be a Use from the
second instruction to the first.

This attempts to fix that by reversing the order of instruction that are sunk,
and ensuring that we update the uses on new instructions if they have already
been sunk, not the old ones.

Differential Revision: https://reviews.llvm.org/D67366

llvm-svn: 371743

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index aebfa2e..b3a6e28 100644 (file)
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -6191,35 +6191,49 @@ bool CodeGenPrepare::tryToSinkFreeOperands(Instruction *I) {
 
   // OpsToSink can contain multiple uses in a use chain (e.g.
   // (%u1 with %u1 = shufflevector), (%u2 with %u2 = zext %u1)). The dominating
-  // uses must come first, which means they are sunk first, temporarily creating
-  // invalid IR. This will be fixed once their dominated users are sunk and
-  // updated.
+  // uses must come first, so we process the ops in reverse order so as to not
+  // create invalid IR.
   BasicBlock *TargetBB = I->getParent();
   bool Changed = false;
   SmallVector<Use *, 4> ToReplace;
-  for (Use *U : OpsToSink) {
+  for (Use *U : reverse(OpsToSink)) {
     auto *UI = cast<Instruction>(U->get());
     if (UI->getParent() == TargetBB || isa<PHINode>(UI))
       continue;
     ToReplace.push_back(U);
   }
 
-  SmallPtrSet<Instruction *, 4> MaybeDead;
+  SetVector<Instruction *> MaybeDead;
+  DenseMap<Instruction *, Instruction *> NewInstructions;
+  Instruction *InsertPoint = I;
   for (Use *U : ToReplace) {
     auto *UI = cast<Instruction>(U->get());
     Instruction *NI = UI->clone();
+    NewInstructions[UI] = NI;
     MaybeDead.insert(UI);
     LLVM_DEBUG(dbgs() << "Sinking " << *UI << " to user " << *I << "\n");
-    NI->insertBefore(I);
+    NI->insertBefore(InsertPoint);
+    InsertPoint = NI;
     InsertedInsts.insert(NI);
-    U->set(NI);
+
+    // Update the use for the new instruction, making sure that we update the
+    // sunk instruction uses, if it is part of a chain that has already been
+    // sunk.
+    Instruction *OldI = cast<Instruction>(U->getUser());
+    if (NewInstructions.count(OldI))
+      NewInstructions[OldI]->setOperand(U->getOperandNo(), NI);
+    else
+      U->set(NI);
     Changed = true;
   }
 
   // Remove instructions that are dead after sinking.
-  for (auto *I : MaybeDead)
-    if (!I->hasNUsesOrMore(1))
+  for (auto *I : MaybeDead) {
+    if (!I->hasNUsesOrMore(1)) {
+      LLVM_DEBUG(dbgs() << "Removing dead instruction: " << *I << "\n");
       I->eraseFromParent();
+    }
+  }
 
   return Changed;
 }

diff --git a/llvm/test/Transforms/CodeGenPrepare/ARM/sink-add-mul-shufflevector.ll b/llvm/test/Transforms/CodeGenPrepare/ARM/sink-add-mul-shufflevector.ll
index 739877b..cb0737f 100644 (file)
--- a/llvm/test/Transforms/CodeGenPrepare/ARM/sink-add-mul-shufflevector.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/ARM/sink-add-mul-shufflevector.ll
@@ -45,9 +45,12 @@ define void @sink_add_mul_multiple(i32* %s1, i32* %s2, i32 %x, i32* %d, i32* %d2
 ; CHECK-NOT:  [[BROADCAST_SPLATINSERT8:%.*]] = insertelement <4 x i32> undef, i32 [[X:%.*]], i32 0
 ; CHECK-NOT:  [[BROADCAST_SPLAT9:%.*]] = shufflevector <4 x i32> [[BROADCAST_SPLATINSERT8]], <4 x i32> undef, <4 x i32> zeroinitializer
 ; CHECK:    vector.body:
-; CHECK:      [[TMP2:%.*]] = insertelement <4 x i32> undef, i32 [[X:%.*]], i32 0
+; CHECK:      [[TMP2:%.*]] = insertelement <4 x i32> undef, i32 %x, i32 0
 ; CHECK:      [[TMP3:%.*]] = shufflevector <4 x i32> [[TMP2]], <4 x i32> undef, <4 x i32> zeroinitializer
-; CHECK:      [[TMP11:%.*]] = shufflevector <4 x i32> [[TMP2]], <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK:      mul nsw <4 x i32> %wide.load, [[TMP3]]
+; CHECK:      [[TMP2b:%.*]] = insertelement <4 x i32> undef, i32 %x, i32 0
+; CHECK:      [[TMP3b:%.*]] = shufflevector <4 x i32> [[TMP2b]], <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK:      mul nsw <4 x i32> %wide.load18, [[TMP3b]]
 ;
 entry:
   %cmp13 = icmp sgt i32 %n, 0

diff --git a/llvm/test/Transforms/CodeGenPrepare/ARM/sinkchain.ll b/llvm/test/Transforms/CodeGenPrepare/ARM/sinkchain.ll
new file mode 100644 (file)
index 0000000..c0da3eb
--- /dev/null
+++ b/llvm/test/Transforms/CodeGenPrepare/ARM/sinkchain.ll
@@ -0,0 +1,107 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -mtriple=thumbv8.1m.main-arm-none-eabi -mattr=+mve.fp < %s -codegenprepare -S | FileCheck -check-prefix=CHECK %s
+
+; Sink the shufflevector/insertelement pair, followed by the trunc. The sunk instruction end up dead.
+define signext i8 @dead(i16* noalias nocapture readonly %s1, i16 zeroext %x, i8* noalias nocapture %d, i32 %n) {
+; CHECK-LABEL: @dead(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[N_VEC:%.*]] = and i32 [[N:%.*]], -8
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i16 [[X:%.*]] to i8
+; CHECK-NEXT:    [[L6:%.*]] = getelementptr inbounds i16, i16* [[S1:%.*]], i32 [[INDEX]]
+; CHECK-NEXT:    [[L7:%.*]] = bitcast i16* [[L6]] to <8 x i16>*
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <8 x i16>, <8 x i16>* [[L7]], align 2
+; CHECK-NEXT:    [[L8:%.*]] = trunc <8 x i16> [[WIDE_LOAD]] to <8 x i8>
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <8 x i8> undef, i8 [[TMP0]], i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <8 x i8> [[TMP1]], <8 x i8> undef, <8 x i32> zeroinitializer
+; CHECK-NEXT:    [[L9:%.*]] = mul <8 x i8> [[TMP2]], [[L8]]
+; CHECK-NEXT:    [[L13:%.*]] = getelementptr inbounds i8, i8* [[D:%.*]], i32 [[INDEX]]
+; CHECK-NEXT:    [[L14:%.*]] = bitcast i8* [[L13]] to <8 x i8>*
+; CHECK-NEXT:    store <8 x i8> [[L9]], <8 x i8>* [[L14]], align 1
+; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 8
+; CHECK-NEXT:    [[L15:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[L15]], label [[EXIT:%.*]], label [[VECTOR_BODY]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i8 0
+;
+entry:
+  %n.vec = and i32 %n, -8
+  %l0 = trunc i16 %x to i8
+  %l1 = insertelement <8 x i8> undef, i8 %l0, i32 0
+  %broadcast.splat26 = shufflevector <8 x i8> %l1, <8 x i8> undef, <8 x i32> zeroinitializer
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %entry
+  %index = phi i32 [ 0, %entry ], [ %index.next, %vector.body ]
+  %l6 = getelementptr inbounds i16, i16* %s1, i32 %index
+  %l7 = bitcast i16* %l6 to <8 x i16>*
+  %wide.load = load <8 x i16>, <8 x i16>* %l7, align 2
+  %l8 = trunc <8 x i16> %wide.load to <8 x i8>
+  %l9 = mul <8 x i8> %broadcast.splat26, %l8
+  %l13 = getelementptr inbounds i8, i8* %d, i32 %index
+  %l14 = bitcast i8* %l13 to <8 x i8>*
+  store <8 x i8> %l9, <8 x i8>* %l14, align 1
+  %index.next = add i32 %index, 8
+  %l15 = icmp eq i32 %index.next, %n.vec
+  br i1 %l15, label %exit, label %vector.body
+
+exit:                                     ; preds = %vector.body
+  ret i8 0
+}
+
+; Same as above, but the shuffle has an extra use meaning it shouldnt be deleted
+define signext i8 @alive(i16* noalias nocapture readonly %s1, i16 zeroext %x, i8* noalias nocapture %d, i32 %n) {
+; CHECK-LABEL: @alive(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[N_VEC:%.*]] = and i32 [[N:%.*]], -8
+; CHECK-NEXT:    [[L0:%.*]] = trunc i16 [[X:%.*]] to i8
+; CHECK-NEXT:    [[L1:%.*]] = insertelement <8 x i8> undef, i8 [[L0]], i32 0
+; CHECK-NEXT:    [[BROADCAST_SPLAT26:%.*]] = shufflevector <8 x i8> [[L1]], <8 x i8> undef, <8 x i32> zeroinitializer
+; CHECK-NEXT:    [[L2:%.*]] = sub <8 x i8> zeroinitializer, [[BROADCAST_SPLAT26]]
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i16 [[X]] to i8
+; CHECK-NEXT:    [[L6:%.*]] = getelementptr inbounds i16, i16* [[S1:%.*]], i32 [[INDEX]]
+; CHECK-NEXT:    [[L7:%.*]] = bitcast i16* [[L6]] to <8 x i16>*
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <8 x i16>, <8 x i16>* [[L7]], align 2
+; CHECK-NEXT:    [[L8:%.*]] = trunc <8 x i16> [[WIDE_LOAD]] to <8 x i8>
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <8 x i8> undef, i8 [[TMP0]], i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <8 x i8> [[TMP1]], <8 x i8> undef, <8 x i32> zeroinitializer
+; CHECK-NEXT:    [[L9:%.*]] = mul <8 x i8> [[TMP2]], [[L8]]
+; CHECK-NEXT:    [[L13:%.*]] = getelementptr inbounds i8, i8* [[D:%.*]], i32 [[INDEX]]
+; CHECK-NEXT:    [[L14:%.*]] = bitcast i8* [[L13]] to <8 x i8>*
+; CHECK-NEXT:    store <8 x i8> [[L9]], <8 x i8>* [[L14]], align 1
+; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 8
+; CHECK-NEXT:    [[L15:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[L15]], label [[EXIT:%.*]], label [[VECTOR_BODY]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i8 0
+;
+entry:
+  %n.vec = and i32 %n, -8
+  %l0 = trunc i16 %x to i8
+  %l1 = insertelement <8 x i8> undef, i8 %l0, i32 0
+  %broadcast.splat26 = shufflevector <8 x i8> %l1, <8 x i8> undef, <8 x i32> zeroinitializer
+  %l2 = sub <8 x i8> zeroinitializer, %broadcast.splat26
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %entry
+  %index = phi i32 [ 0, %entry ], [ %index.next, %vector.body ]
+  %l6 = getelementptr inbounds i16, i16* %s1, i32 %index
+  %l7 = bitcast i16* %l6 to <8 x i16>*
+  %wide.load = load <8 x i16>, <8 x i16>* %l7, align 2
+  %l8 = trunc <8 x i16> %wide.load to <8 x i8>
+  %l9 = mul <8 x i8> %broadcast.splat26, %l8
+  %l13 = getelementptr inbounds i8, i8* %d, i32 %index
+  %l14 = bitcast i8* %l13 to <8 x i8>*
+  store <8 x i8> %l9, <8 x i8>* %l14, align 1
+  %index.next = add i32 %index, 8
+  %l15 = icmp eq i32 %index.next, %n.vec
+  br i1 %l15, label %exit, label %vector.body
+
+exit:                                     ; preds = %vector.body
+  ret i8 0
+}