[SCEV] Do not visit nodes twice in containsConstantSomewhere

This patch reworks the function that searches constants in Add and Mul SCEV expression
chains so that now it does not visit a node more than once, and also renames this function
for better correspondence between its implementation and semantics.

Differential Revision: https://reviews.llvm.org/D35931

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309367 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 4d7b59c476351aa1d8231acbc1e09d50a3fc827f..ecd124a576c40f8289fde814b48ffeda2cb22678 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2676,20 +2676,23 @@ static uint64_t Choose(uint64_t n, uint64_t k, bool &Overflow) {
 
 /// Determine if any of the operands in this SCEV are a constant or if
 /// any of the add or multiply expressions in this SCEV contain a constant.
-static bool containsConstantSomewhere(const SCEV *StartExpr) {
-  SmallVector<const SCEV *, 4> Ops;
-  Ops.push_back(StartExpr);
-  while (!Ops.empty()) {
-    const SCEV *CurrentExpr = Ops.pop_back_val();
-    if (isa<SCEVConstant>(*CurrentExpr))
-      return true;
+static bool containsConstantInAddMulChain(const SCEV *StartExpr) {
+  struct FindConstantInAddMulChain {
+    bool FoundConstant = false;
 
-    if (isa<SCEVAddExpr>(*CurrentExpr) || isa<SCEVMulExpr>(*CurrentExpr)) {
-      const auto *CurrentNAry = cast<SCEVNAryExpr>(CurrentExpr);
-      Ops.append(CurrentNAry->op_begin(), CurrentNAry->op_end());
+    bool follow(const SCEV *S) {
+      FoundConstant |= isa<SCEVConstant>(S);
+      return isa<SCEVAddExpr>(S) || isa<SCEVMulExpr>(S);
     }
-  }
-  return false;
+    bool isDone() const {
+      return FoundConstant;
+    }
+  };
+
+  FindConstantInAddMulChain F;
+  SCEVTraversal<FindConstantInAddMulChain> ST(F);
+  ST.visitAll(StartExpr);
+  return F.FoundConstant;
 }
 
 /// Get a canonical multiply expression, or something simpler if possible.
@@ -2726,7 +2729,11 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
           // If any of Add's ops are Adds or Muls with a constant,
           // apply this transformation as well.
           if (Add->getNumOperands() == 2)
-            if (containsConstantSomewhere(Add))
+            // TODO: There are some cases where this transformation is not
+            // profitable, for example:
+            // Add = (C0 + X) * Y + Z.
+            // Maybe the scope of this transformation should be narrowed down.
+            if (containsConstantInAddMulChain(Add))
               return getAddExpr(getMulExpr(LHSC, Add->getOperand(0),
                                            SCEV::FlagAnyWrap, Depth + 1),
                                 getMulExpr(LHSC, Add->getOperand(1),

diff --git a/test/Transforms/LoopSimplify/pr33494.ll b/test/Transforms/LoopSimplify/pr33494.ll
new file mode 100644 (file)
index 0000000..5d3b4e8
--- /dev/null
+++ b/test/Transforms/LoopSimplify/pr33494.ll
@@ -0,0 +1,75 @@
+; RUN: opt -loop-unroll -loop-simplify -S  < %s | FileCheck %s
+
+; This test is one of the tests of PR33494. Its compilation takes
+; excessive time if we don't mark visited nodes while looking for
+; constants in SCEV expression trees.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test_01(i32* nocapture %a) local_unnamed_addr {
+
+; CHECK-LABEL: @test_01(
+
+entry:
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 96
+  %arrayidx.promoted51 = load i32, i32* %arrayidx, align 1
+  br label %while.body
+
+while.body:                                       ; preds = %entry, %while.end29
+  %0 = phi i32 [ %arrayidx.promoted51, %entry ], [ %7, %while.end29 ]
+  %cmp46 = icmp eq i32 %0, 1
+  %conv47 = zext i1 %cmp46 to i32
+  %1 = add i32 %0, 1
+  %2 = icmp ult i32 %1, 3
+  %div48 = select i1 %2, i32 %0, i32 0
+  %cmp349 = icmp sgt i32 %div48, %conv47
+  br i1 %cmp349, label %while.body4.lr.ph, label %while.end29
+
+while.body4.lr.ph:                                ; preds = %while.body
+  br label %while.body4
+
+while.body4:                                      ; preds = %while.body4.lr.ph, %while.end28
+  %3 = phi i32 [ %0, %while.body4.lr.ph ], [ %mul17.lcssa, %while.end28 ]
+  br label %while.body13
+
+while.body13:                                     ; preds = %while.body4, %while.end.split
+  %mul1745 = phi i32 [ %3, %while.body4 ], [ %mul17, %while.end.split ]
+  %4 = phi i32 [ 15872, %while.body4 ], [ %add, %while.end.split ]
+  %mul = mul nsw i32 %mul1745, %mul1745
+  %mul17 = mul nsw i32 %mul, %mul1745
+  %cmp22 = icmp eq i32 %4, %mul17
+  br i1 %cmp22, label %while.body13.split, label %while.end.split
+
+while.body13.split:                               ; preds = %while.body13
+  br label %while.cond19
+
+while.cond19:                                     ; preds = %while.cond19, %while.body13.split
+  br label %while.cond19
+
+while.end.split:                                  ; preds = %while.body13
+  %add = shl nsw i32 %4, 1
+  %tobool12 = icmp eq i32 %add, 0
+  br i1 %tobool12, label %while.end28, label %while.body13
+
+while.end28:                                      ; preds = %while.end.split
+  %add.lcssa = phi i32 [ %add, %while.end.split ]
+  %mul17.lcssa = phi i32 [ %mul17, %while.end.split ]
+  %cmp = icmp eq i32 %mul17.lcssa, 1
+  %conv = zext i1 %cmp to i32
+  %5 = add i32 %mul17.lcssa, 1
+  %6 = icmp ult i32 %5, 3
+  %div = select i1 %6, i32 %mul17.lcssa, i32 0
+  %cmp3 = icmp sgt i32 %div, %conv
+  br i1 %cmp3, label %while.body4, label %while.cond1.while.end29_crit_edge
+
+while.cond1.while.end29_crit_edge:                ; preds = %while.end28
+  %.lcssa = phi i32 [ %mul17.lcssa, %while.end28 ]
+  %add.lcssa50.lcssa = phi i32 [ %add.lcssa, %while.end28 ]
+  store i32 %add.lcssa50.lcssa, i32* %a, align 4
+  br label %while.end29
+
+while.end29:                                      ; preds = %while.cond1.while.end29_crit_edge, %while.body
+  %7 = phi i32 [ %.lcssa, %while.cond1.while.end29_crit_edge ], [ %0, %while.body ]
+  br label %while.body
+}