getSmallConstantTripMultiple should never return zero.

When the trip count is -1, getSmallConstantTripMultiple could return zero,
and this would cause runtime loop unrolling to assert. Instead of returning
zero, one is now returned (consistent with the existing overflow cases).
Fixes PR14167.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166612 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 3e062988823277c261917210099d8e0309d8db5d..148912b766b25e222efc7730bb67d547c0e73373 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3979,8 +3979,11 @@ getSmallConstantTripMultiple(Loop *L, BasicBlock *ExitingBlock) {
 
   ConstantInt *Result = MulC->getValue();
 
-  // Guard against huge trip counts.
-  if (!Result || Result->getValue().getActiveBits() > 32)
+  // Guard against huge trip counts (this requires checking
+  // for zero to handle the case where the trip count == -1 and the
+  // addition wraps).
+  if (!Result || Result->getValue().getActiveBits() > 32 ||
+      Result->getValue().getActiveBits() == 0)
     return 1;
 
   return (unsigned)Result->getZExtValue();

diff --git a/test/Transforms/LoopUnroll/pr14167.ll b/test/Transforms/LoopUnroll/pr14167.ll
new file mode 100644 (file)
index 0000000..205ae44
--- /dev/null
+++ b/test/Transforms/LoopUnroll/pr14167.ll
@@ -0,0 +1,44 @@
+; RUN: opt < %s -S -loop-unroll -unroll-runtime | 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-v128:128:128-n32:64"
+target triple = "powerpc64-bgq-linux"
+
+define void @test1() nounwind {
+; Ensure that we don't crash when the trip count == -1.
+; CHECK: @test1
+entry:
+  br label %for.cond2.preheader
+
+for.cond2.preheader:                              ; preds = %for.end, %entry
+  br i1 false, label %middle.block, label %vector.ph
+
+vector.ph:                                        ; preds = %for.cond2.preheader
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %vector.ph
+  br i1 undef, label %middle.block.loopexit, label %vector.body
+
+middle.block.loopexit:                            ; preds = %vector.body
+  br label %middle.block
+
+middle.block:                                     ; preds = %middle.block.loopexit, %for.cond2.preheader
+  br i1 true, label %for.end, label %scalar.preheader
+
+scalar.preheader:                                 ; preds = %middle.block
+  br label %for.body4
+
+for.body4:                                        ; preds = %for.body4, %scalar.preheader
+  %indvars.iv = phi i64 [ 16000, %scalar.preheader ], [ %indvars.iv.next, %for.body4 ]
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp ne i32 %lftr.wideiv, 16000
+  br i1 %exitcond, label %for.body4, label %for.end.loopexit
+
+for.end.loopexit:                                 ; preds = %for.body4
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %middle.block
+  br i1 undef, label %for.cond2.preheader, label %for.end15
+
+for.end15:                                        ; preds = %for.end
+  ret void
+}