From: Chandler Carruth <chandlerc@gmail.com>
Date: Mon, 6 Feb 2017 21:27:12 +0000 (+0000)
Subject: [SCEV] Scale back the test added in r294181 as it goes quadratic in
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8425f9249757fa16076ce6b1c269a4b6f9253291;p=llvm

[SCEV] Scale back the test added in r294181 as it goes quadratic in
SCEV.

This test was immediately the slowest test in 'check-llvm' even in an
optimized build and was driving up the total test time by 50% for me.

Sanjoy has filed a PR about the quadratic behavior in SCEV but it is
also concerning that the test still passes given that r294181 added
a threshold at 32 to SCEV. I've followed up on the original patch to
figure out how this test should work long-term, but for now I want to
get check-llvm to be fast again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294241 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/unittests/Analysis/ScalarEvolutionTest.cpp b/unittests/Analysis/ScalarEvolutionTest.cpp
index 52368a89884..a9b144c5011 100644
--- a/unittests/Analysis/ScalarEvolutionTest.cpp
+++ b/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -549,7 +549,11 @@ TEST_F(ScalarEvolutionsTest, SCEVAddExpr) {
   Instruction *Add1 = BinaryOperator::CreateAdd(Mul1, Trunc, "", EntryBB);
   Mul1 = BinaryOperator::CreateMul(Add1, Trunc, "", EntryBB);
   Instruction *Add2 = BinaryOperator::CreateAdd(Mul1, Add1, "", EntryBB);
-  for (int i = 0; i < 1000; i++) {
+  // FIXME: The size of this is arbitrary and doesn't seem to change the
+  // result, but SCEV will do quadratic work for these so a large number here
+  // will be extremely slow. We should revisit what and how this is testing
+  // SCEV.
+  for (int i = 0; i < 10; i++) {
     Mul1 = BinaryOperator::CreateMul(Add2, Add1, "", EntryBB);
     Add1 = Add2;
     Add2 = BinaryOperator::CreateAdd(Mul1, Add1, "", EntryBB);