If the step value is a constant zero, the loop isn't going to terminate. Fixes

the assert reported in PR13228!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159393 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 886812be5faa58a76bfb0af8590b45ff3fd47ace..09410496d31ac957af1d2aeae35307b10a6c7a67 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -5484,7 +5484,7 @@ ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) {
   // to 0, it must be counting down to equal 0. Consequently, N = Start / -Step.
   // We have not yet seen any such cases.
   const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
-  if (StepC == 0)
+  if (StepC == 0 || StepC->getValue()->equalsInt(0))
     return getCouldNotCompute();
 
   // For positive steps (counting up until unsigned overflow):

diff --git a/test/Analysis/ScalarEvolution/how-far-to-zero.ll b/test/Analysis/ScalarEvolution/how-far-to-zero.ll
new file mode 100644 (file)
index 0000000..07af88f
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/how-far-to-zero.ll
@@ -0,0 +1,27 @@
+; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
+
+; PR13228
+define void @f() nounwind uwtable readnone {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %c.0 = phi i8 [ 1, %entry ], [ 0, %for.cond ]
+  %i.0 = phi i8 [ 0, %entry ], [ %inc, %for.cond ]
+  %lnot = icmp eq i8 %i.0, 0
+  %inc = add i8 %i.0, 1
+  br i1 %lnot, label %for.cond, label %while.cond
+
+while.cond:                                       ; preds = %while.body, %for.cond
+  %b.2 = phi i8 [ %add, %while.body ], [ 0, %for.cond ]
+  br i1 undef, label %while.end, label %while.body
+
+while.body:                                       ; preds = %while.cond
+  %add = add i8 %b.2, %c.0
+  %tobool7 = icmp eq i8 %add, 0
+  br i1 %tobool7, label %while.end, label %while.cond
+
+while.end:                                        ; preds = %while.body, %while.cond
+  ret void
+}
+;CHECK: Loop %while.cond: <multiple exits> Unpredictable backedge-taken count.