From b92654d9c9cc34c75463e40d822fea4ac53950b3 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Sat, 19 Jun 2010 14:17:24 +0000
Subject: [PATCH] Fix ScalarEvolution's "exhaustive" trip count evaluation code
 to avoid assuming that loops are in canonical form, as ScalarEvolution
 doesn't depend on LoopSimplify itself. Also, with indirectbr not all loops
 can be simplified. This fixes PR7416.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106389 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              |  7 +++--
 test/Analysis/ScalarEvolution/trip-count10.ll | 31 +++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 7e7fc756d10..251b57a0f98 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -4238,8 +4238,11 @@ ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
   PHINode *PN = getConstantEvolvingPHI(Cond, L);
   if (PN == 0) return getCouldNotCompute();
 
-  // Since the loop is canonicalized, the PHI node must have two entries.  One
-  // entry must be a constant (coming in from outside of the loop), and the
+  // If the loop is canonicalized, the PHI will have exactly two entries.
+  // That's the only form we support here.
+  if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
+
+  // One entry must be a constant (coming in from outside of the loop), and the
   // second must be derived from the same PHI.
   bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1));
   Constant *StartCST =
diff --git a/test/Analysis/ScalarEvolution/trip-count10.ll b/test/Analysis/ScalarEvolution/trip-count10.ll
index 0a992f952a8..2386cf4f597 100644
--- a/test/Analysis/ScalarEvolution/trip-count10.ll
+++ b/test/Analysis/ScalarEvolution/trip-count10.ll
@@ -74,3 +74,34 @@ loop:
 return:
   ret void
 }
+
+; Trip counts for non-polynomial iterations. It's theoretically possible
+; to compute a maximum count for these, but short of that, ScalarEvolution
+; should return unknown.
+
+; PR7416
+; CHECK: Determining loop execution counts for: @nonpolynomial
+; CHECK-NEXT: Loop %loophead: Unpredictable backedge-taken count
+; CHECK-NEXT: Loop %loophead: Unpredictable max backedge-taken count
+
+declare i1 @g() nounwind
+
+define void @nonpolynomial() {
+entry:
+  br label %loophead
+loophead:
+  %x = phi i32 [0, %entry], [%x.1, %bb1], [%x.2, %bb2]
+  %y = icmp slt i32 %x, 100
+  br i1 %y, label %loopbody, label %retbb
+loopbody:
+  %z = call i1 @g()
+  br i1 %z, label %bb1, label %bb2
+bb1:
+  %x.1 = add i32 %x, 2
+  br label %loophead
+bb2:
+  %x.2 = add i32 %x, 3
+  br label %loophead
+retbb:
+  ret void
+}