From 3846163aee1b14545057c8664f80a18c55309462 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Mon, 24 Oct 2011 21:02:38 +0000
Subject: [PATCH] Now that we look at all the header PHIs, we need to consider
 all the header PHIs when deciding that the loop has stopped evolving. Fixes
 miscompile in the gcc torture testsuite!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142843 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              | 20 +++++++++----
 test/Analysis/ScalarEvolution/trip-count11.ll | 29 +++++++++++++++++++
 2 files changed, 43 insertions(+), 6 deletions(-)
 create mode 100644 test/Analysis/ScalarEvolution/trip-count11.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 1ab6a406fce..f65cf343355 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -4844,12 +4844,12 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
     // EvaluateExpression adds non-phi values to the CurrentIterVals map.
     DenseMap<Instruction *, Constant *> NextIterVals;
     Constant *NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
-    if (NextPHI == CurrentIterVals[PN])
-      return RetVal = NextPHI;  // Stopped evolving!
     if (NextPHI == 0)
       return 0;        // Couldn't evaluate!
     NextIterVals[PN] = NextPHI;
 
+    bool StoppedEvolving = NextPHI == CurrentIterVals[PN];
+
     // Also evaluate the other PHI nodes.  However, we don't get to stop if we
     // cease to be able to evaluate one of them or if they stop evolving,
     // because that doesn't necessarily prevent us from computing PN.
@@ -4858,11 +4858,19 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
       PHINode *PHI = dyn_cast<PHINode>(I->first);
       if (!PHI || PHI == PN || PHI->getParent() != Header) continue;
       Constant *&NextPHI = NextIterVals[PHI];
-      if (NextPHI) continue;    // Already computed!
-
-      Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
-      NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
+      if (!NextPHI) {   // Not already computed.
+        Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
+        NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
+      }
+      if (NextPHI != I->second)
+        StoppedEvolving = false;
     }
+
+    // If all entries in CurrentIterVals == NextIterVals then we can stop
+    // iterating, the loop can't continue to change.
+    if (StoppedEvolving)
+      return RetVal = CurrentIterVals[PN];
+
     CurrentIterVals.swap(NextIterVals);
   }
 }
diff --git a/test/Analysis/ScalarEvolution/trip-count11.ll b/test/Analysis/ScalarEvolution/trip-count11.ll
new file mode 100644
index 00000000000..71915037ec8
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/trip-count11.ll
@@ -0,0 +1,29 @@
+; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
+
+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"
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo.a = internal constant [8 x i32] [i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7], align 16
+
+define i32 @foo() nounwind uwtable noinline {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %sum.0 = phi i32 [ 0, %entry ], [ %add, %for.inc ]
+; CHECK: --> %sum.0 Exits: 28
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp ult i32 %i.0, 8
+  br i1 %cmp, label %for.inc, label %for.end
+
+for.inc:                                          ; preds = %for.cond
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds [8 x i32]* @foo.a, i64 0, i64 %idxprom
+  %0 = load i32* %arrayidx, align 4
+  %add = add nsw i32 %sum.0, %0
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret i32 %sum.0
+}