Test case and comment for PR9633.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130294 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 9396b07dab923c8639d09bf3e00723cbcd170317..1bef857e70aa5fed6dffb6b5b725ff8c066e015e 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -4705,8 +4705,9 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
         getAddRecExpr(NewOps, AddRec->getLoop(),
                       AddRec->getNoWrapFlags(SCEV::FlagNW));
       AddRec = dyn_cast<SCEVAddRecExpr>(FoldedRec);
-      // In cases with "undef" values, a loop's own recurrence may
-      // fold into a constant. Go ahead and return the optimistic value.
+      // The addrec may be folded to a nonrecurrence, for example, if the
+      // induction variable is multiplied by zero after constant folding. Go
+      // ahead and return the folded value.
       if (!AddRec)
         return FoldedRec;
       break;

diff --git a/test/Analysis/ScalarEvolution/2011-04-26-FoldAddRec.ll b/test/Analysis/ScalarEvolution/2011-04-26-FoldAddRec.ll
new file mode 100644 (file)
index 0000000..1600d5f
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/2011-04-26-FoldAddRec.ll
@@ -0,0 +1,33 @@
+; RUN: opt < %s -analyze -iv-users
+; PR9633: Tests that SCEV handles the mul.i2 recurrence being folded to
+; constant zero.
+
+define signext i8 @func_14(i8 signext %p_18) nounwind readnone ssp {
+entry:
+  br label %for.inc
+
+for.inc:
+  %p_17.addr.012 = phi i32 [ 0, %entry ], [ %add, %for.inc ]
+  %add = add nsw i32 %p_17.addr.012, 1
+  br i1 false, label %for.inc, label %for.cond
+
+for.cond:
+  %tobool.i = icmp ult i32 %add, 8192
+  %shl.i = select i1 %tobool.i, i32 13, i32 0
+  %shl.left.i = shl i32 %add, %shl.i
+  %conv.i4 = trunc i32 %shl.left.i to i8
+  br i1 undef, label %for.inc9, label %if.then
+
+for.inc9:
+  %p_18.addr.011 = phi i8 [ %add12, %for.inc9 ], [ %p_18, %for.cond ]
+  %add12 = add i8 %p_18.addr.011, 1
+  %mul.i2 = mul i8 %add12, %conv.i4
+  %mul.i2.lobit = lshr i8 %mul.i2, 7
+  %lor.ext.shr.i = select i1 undef, i8 %mul.i2.lobit, i8 %mul.i2
+  %tobool = icmp eq i8 %lor.ext.shr.i, 0
+  br i1 %tobool, label %for.inc9, label %if.then
+
+if.then:
+  ret i8 0
+
+}
\ No newline at end of file