Revert "[LV] Extend trunc optimization to all IVs with constant integer steps"

This reverts commit r294967. This patch caused execution time slowdowns in a
few LLVM test-suite tests, as reported by the clang-cmake-aarch64-quick bot.
I'm reverting to investigate.

llvm-svn: 294973

Author: mssimpso

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4879,15 +4879,12 @@ void InnerLoopVectorizer::vectorizeBlockInLoop(BasicBlock *BB, PhiVector *PV) {
       // induction variable. Notice that we can only optimize the 'trunc' case
       // because (a) FP conversions lose precision, (b) sext/zext may wrap, and
       // (c) other casts depend on pointer size.
-      if (auto *Trunc = dyn_cast<TruncInst>(CI))
-        if (auto *Phi = dyn_cast<PHINode>(Trunc->getOperand(0))) {
-          auto II = Legal->getInductionVars()->find(Phi);
-          if (II != Legal->getInductionVars()->end())
-            if (II->second.getConstIntStepValue()) {
-              widenIntInduction(Phi, Trunc);
-              break;
-            }
-        }
+      auto ID = Legal->getInductionVars()->lookup(OldInduction);
+      if (isa<TruncInst>(CI) && CI->getOperand(0) == OldInduction &&
+          ID.getConstIntStepValue()) {
+        widenIntInduction(OldInduction, cast<TruncInst>(CI));
+        break;
+      }
 
       /// Vectorize casts.
       Type *DestTy =
@@ -7227,17 +7224,12 @@ unsigned LoopVectorizationCostModel::getInstructionCost(Instruction *I,
   case Instruction::Trunc:
   case Instruction::FPTrunc:
   case Instruction::BitCast: {
-    // We optimize the truncation of induction variables having constant
-    // integer steps. The cost of these truncations is the same as the scalar
-    // operation.
-    if (auto *Trunc = dyn_cast<TruncInst>(I))
-      if (auto *Phi = dyn_cast<PHINode>(Trunc->getOperand(0))) {
-        auto II = Legal->getInductionVars()->find(Phi);
-        if (II != Legal->getInductionVars()->end())
-          if (II->second.getConstIntStepValue())
-            return TTI.getCastInstrCost(Instruction::Trunc, Trunc->getDestTy(),
-                                        Trunc->getSrcTy());
-      }
+    // We optimize the truncation of induction variable.
+    // The cost of these is the same as the scalar operation.
+    if (I->getOpcode() == Instruction::Trunc &&
+        Legal->isInductionVariable(I->getOperand(0)))
+      return TTI.getCastInstrCost(I->getOpcode(), I->getType(),
+                                  I->getOperand(0)->getType());
 
     Type *SrcScalarTy = I->getOperand(0)->getType();
     Type *SrcVecTy = ToVectorTy(SrcScalarTy, VF);

llvm/test/Transforms/LoopVectorize/induction.ll

@@ -773,34 +773,3 @@ for.body:
 exit:
   ret void
 }
-
-; CHECK-LABEL: @non_primary_iv_trunc(
-; CHECK:       vector.body:
-; CHECK-NEXT:    %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
-; CHECK:         [[VEC_IND:%.*]] = phi <2 x i32> [ <i32 0, i32 2>, %vector.ph ], [ [[VEC_IND_NEXT:%.*]], %vector.body ]
-; CHECK:         [[TMP3:%.*]] = add i64 %index, 0
-; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr inbounds i32, i32* %a, i64 [[TMP3]]
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr i32, i32* [[TMP4]], i32 0
-; CHECK-NEXT:    [[TMP6:%.*]] = bitcast i32* [[TMP5]] to <2 x i32>*
-; CHECK-NEXT:    store <2 x i32> [[VEC_IND]], <2 x i32>* [[TMP6]], align 4
-; CHECK-NEXT:    %index.next = add i64 %index, 2
-; CHECK:         [[VEC_IND_NEXT]] = add <2 x i32> [[VEC_IND]], <i32 4, i32 4>
-; CHECK:         br i1 {{.*}}, label %middle.block, label %vector.body
-define void @non_primary_iv_trunc(i32* %a, i64 %n) {
-entry:
-  br label %for.body
-
-for.body:
-  %i = phi i64 [ %i.next, %for.body ], [ 0, %entry ]
-  %j = phi i64 [ %j.next, %for.body ], [ 0, %entry ]
-  %tmp0 = getelementptr inbounds i32, i32* %a, i64 %i
-  %tmp1 = trunc i64 %j to i32
-  store i32 %tmp1, i32* %tmp0, align 4
-  %i.next = add nuw nsw i64 %i, 1
-  %j.next = add nuw nsw i64 %j, 2
-  %cond = icmp slt i64 %i.next, %n
-  br i1 %cond, label %for.body, label %for.end
-
-for.end:
-  ret void
-}

llvm/test/Transforms/LoopVectorize/reverse_iter.ll

@@ -2,8 +2,7 @@
 
 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-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
-; PR15882: This test ensures that we do not produce wrapping arithmetic when
-; creating constant reverse step vectors.
+; Make sure that the reverse iterators are calculated using 64bit arithmetic, not 32.
 ;
 ; int foo(int n, int *A) {
 ;   int sum;
@@ -14,7 +13,7 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
 ;
 
 ;CHECK-LABEL: @foo(
-;CHECK:  <i32 0, i32 -1, i32 -2, i32 -3>
+;CHECK:  <i64 0, i64 -1, i64 -2, i64 -3>
 ;CHECK: ret
 define i32 @foo(i32 %n, i32* nocapture %A) {
   %1 = icmp sgt i32 %n, 0