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

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 1ab6a406fce04f2cc245b0b3849c944c572e1dc6..f65cf3433550afba208b88ed54d97ebb29719438 100644 (file)
--- 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 (file)
index 0000000..7191503
--- /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
+}