[llvm-commits] [llvm] r159393 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/how-far-to-zero.ll

[Nick Lewycky]

Author: nicholas
Date: Thu Jun 28 18:44:57 2012
New Revision: 159393

URL: http://llvm.org/viewvc/llvm-project?rev=159393&view=rev
Log:
If the step value is a constant zero, the loop isn't going to terminate. Fixes
the assert reported in PR13228!

Added:
    llvm/trunk/test/Analysis/ScalarEvolution/how-far-to-zero.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=159393&r1=159392&r2=159393&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Jun 28 18:44:57 2012
@@ -5484,7 +5484,7 @@
   // 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):

Added: llvm/trunk/test/Analysis/ScalarEvolution/how-far-to-zero.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/how-far-to-zero.ll?rev=159393&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/how-far-to-zero.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/how-far-to-zero.ll Thu Jun 28 18:44:57 2012
@@ -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.