Fixes PR2395. Looking for a constant in a GEP tail (when the first GEP

is longer than the second one) should stop after finding one. Added break
instruction guarantees it. It also changes difference between offsets to
absolute value of this difference in the condition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51875 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 21108c645351c71ec7c079ad52b99f0519e3f5ed..599a6f650fd3da4afa5ba3e31c094e6c3554ae0c 100644 (file)
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -687,7 +687,7 @@ BasicAliasAnalysis::CheckGEPInstructions(
         if (isa<ConstantInt>(GEP1Ops[i]) && 
             !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
           // Yup, there's a constant in the tail.  Set all variables to
-          // constants in the GEP instruction to make it suiteable for
+          // constants in the GEP instruction to make it suitable for
           // TargetData::getIndexedOffset.
           for (i = 0; i != MaxOperands; ++i)
             if (!isa<ConstantInt>(GEP1Ops[i]))
@@ -702,9 +702,15 @@ BasicAliasAnalysis::CheckGEPInstructions(
           int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
                                                 MinOperands);
 
+          // Make sure we compare the absolute difference.
+          if (Offset1 > Offset2)
+            std::swap(Offset1, Offset2);
+
           // If the tail provided a bit enough offset, return noalias!
           if ((uint64_t)(Offset2-Offset1) >= SizeMax)
             return NoAlias;
+          // Otherwise break - we don't look for another constant in the tail.
+          break;
         }
     }
 

diff --git a/test/Analysis/BasicAA/2008-06-02-GEPTailCrash.ll b/test/Analysis/BasicAA/2008-06-02-GEPTailCrash.ll
new file mode 100644 (file)
index 0000000..40d1e32
--- /dev/null
+++ b/test/Analysis/BasicAA/2008-06-02-GEPTailCrash.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | opt -gvn -disable-output
+; PR2395
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
+target triple = "i686-pc-linux-gnu"
+       %struct.S291 = type <{ %union.anon, i32 }>
+       %union.anon = type {  }
+@a291 = external global [5 x %struct.S291]             ; <[5 x %struct.S291]*> [#uses=2]
+
+define void @test291() nounwind  {
+entry:
+       store i32 1138410269, i32* getelementptr ([5 x %struct.S291]* @a291, i32 0, i32 2, i32 1)
+       %tmp54 = load i32* bitcast (%struct.S291* getelementptr ([5 x %struct.S291]* @a291, i32 0, i32 2) to i32*), align 4             ; <i32> [#uses=0]
+       unreachable
+}