[llvm-commits] [llvm] r140992 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/max-trip-count.ll

[Nick Lewycky]

Author: nicholas
Date: Mon Oct  3 02:10:45 2011
New Revision: 140992

URL: http://llvm.org/viewvc/llvm-project?rev=140992&view=rev
Log:
Reapply r140979 with fix! We never did get a testcase, but careful review of the
logic by David Meyer revealed this bug.

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/max-trip-count.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=140992&r1=140991&r2=140992&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Oct  3 02:10:45 2011
@@ -5119,7 +5119,7 @@
     // Compute the two solutions for the quadratic formula.
     // The divisions must be performed as signed divisions.
     APInt NegB(-B);
-    APInt TwoA( A << 1 );
+    APInt TwoA(A << 1);
     if (TwoA.isMinValue()) {
       const SCEV *CNC = SE.getCouldNotCompute();
       return std::make_pair(CNC, CNC);
@@ -5134,7 +5134,7 @@
 
     return std::make_pair(SE.getConstant(Solution1),
                           SE.getConstant(Solution2));
-    } // end APIntOps namespace
+  } // end APIntOps namespace
 }
 
 /// HowFarToZero - Return the number of times a backedge comparing the specified
@@ -5228,8 +5228,19 @@
   // Handle unitary steps, which cannot wraparound.
   // 1*N = -Start; -1*N = Start (mod 2^BW), so:
   //   N = Distance (as unsigned)
-  if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue())
-    return Distance;
+  if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue()) {
+    ConstantRange CR = getUnsignedRange(Start);
+    const SCEV *MaxBECount;
+    if (!CountDown && CR.getUnsignedMin().isMinValue())
+      // When counting up, the worst starting value is 1, not 0.
+      MaxBECount = CR.getUnsignedMax().isMinValue()
+        ? getConstant(APInt::getMinValue(CR.getBitWidth()))
+        : getConstant(APInt::getMaxValue(CR.getBitWidth()));
+    else
+      MaxBECount = getConstant(CountDown ? CR.getUnsignedMax()
+                                         : -CR.getUnsignedMin());
+    return ExitLimit(Distance, MaxBECount);
+  }
 
   // If the recurrence is known not to wraparound, unsigned divide computes the
   // back edge count. We know that the value will either become zero (and thus

Modified: llvm/trunk/test/Analysis/ScalarEvolution/max-trip-count.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/max-trip-count.ll?rev=140992&r1=140991&r2=140992&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/max-trip-count.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/max-trip-count.ll Mon Oct  3 02:10:45 2011
@@ -70,3 +70,31 @@
 }
 
 declare i32 @printf(i8*, ...)
+
+define void @test(i8* %a, i32 %n) nounwind {
+entry:
+  %cmp1 = icmp sgt i32 %n, 0
+  br i1 %cmp1, label %for.body.lr.ph, label %for.end
+
+for.body.lr.ph:                                   ; preds = %entry
+  %tmp = zext i32 %n to i64
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.lr.ph
+  %indvar = phi i64 [ %indvar.next, %for.body ], [ 0, %for.body.lr.ph ]
+  %arrayidx = getelementptr i8* %a, i64 %indvar
+  store i8 0, i8* %arrayidx, align 1
+  %indvar.next = add i64 %indvar, 1
+  %exitcond = icmp ne i64 %indvar.next, %tmp
+  br i1 %exitcond, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge:                       ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond.for.end_crit_edge, %entry
+  ret void
+}
+
+; CHECK: Determining loop execution counts for: @test
+; CHECK-NEXT: backedge-taken count is
+; CHECK-NEXT: max backedge-taken count is -1