[llvm-commits] [llvm] r166612 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Transforms/LoopUnroll/pr14167.ll

[Hal Finkel]

Author: hfinkel
Date: Wed Oct 24 14:46:44 2012
New Revision: 166612

URL: http://llvm.org/viewvc/llvm-project?rev=166612&view=rev
Log:
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.

Added:
    llvm/trunk/test/Transforms/LoopUnroll/pr14167.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=166612&r1=166611&r2=166612&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Oct 24 14:46:44 2012
@@ -3979,8 +3979,11 @@
 
   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();

Added: llvm/trunk/test/Transforms/LoopUnroll/pr14167.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/pr14167.ll?rev=166612&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/pr14167.ll (added)
+++ llvm/trunk/test/Transforms/LoopUnroll/pr14167.ll Wed Oct 24 14:46:44 2012
@@ -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
+}