SCEV fix: Handle loop invariant loads.

Fixes PR11882: NULL dereference in ComputeLoadConstantCompareExitLimit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153480 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ScalarEvolution.cpp

@@ -4619,6 +4619,10 @@ ScalarEvolution::ComputeLoadConstantCompareExitLimit(
       Indexes.push_back(0);
     }
 
+  // Loop-invariant loads may be a byproduct of loop optimization. Skip them.
+  if (!VarIdx)
+    return getCouldNotCompute();
+
   // Okay, we know we have a (load (gep GV, 0, X)) comparison with a constant.
   // Check to see if X is a loop variant variable value now.
   const SCEV *Idx = getSCEV(VarIdx);
@@ -6845,7 +6849,7 @@ ScalarEvolution::computeBlockDisposition(const SCEV *S, const BasicBlock *BB) {
     return ProperlyDominatesBlock;
   case scCouldNotCompute:
     llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
-  default: 
+  default:
     llvm_unreachable("Unknown SCEV kind!");
   }
 }

test/Analysis/ScalarEvolution/2012-03-26-LoadConstant.ll

@@ -0,0 +1,47 @@
+; RUN: opt < %s -basicaa -globalopt -instcombine -loop-rotate -licm -instcombine -indvars -loop-deletion -constmerge -S
+; PR11882: ComputeLoadConstantCompareExitLimit crash.
+;
+; for.body is deleted leaving a loop-invariant load.
+; CHECK-NOT: for.body
+target datalayout = "e-p:64:64:64-n32:64"
+
+@func_21_l_773 = external global i32, align 4
+@g_814 = external global i32, align 4
+@g_244 = internal global [1 x [0 x i32]] zeroinitializer, align 4
+
+define void @func_21() nounwind uwtable ssp {
+entry:
+  br label %lbl_818
+
+lbl_818:                                          ; preds = %for.end, %entry
+  call void (...)* @func_27()
+  store i32 0, i32* @g_814, align 4, !tbaa !0
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %lbl_818
+  %0 = load i32* @g_814, align 4, !tbaa !0
+  %cmp = icmp sle i32 %0, 0
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %idxprom = sext i32 %0 to i64
+  %arrayidx = getelementptr inbounds [0 x i32]* getelementptr inbounds ([1 x [0 x i32]]* @g_244, i32 0, i64 0), i32 0, i64 %idxprom
+  %1 = load i32* %arrayidx, align 1, !tbaa !0
+  store i32 %1, i32* @func_21_l_773, align 4, !tbaa !0
+  store i32 1, i32* @g_814, align 4, !tbaa !0
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  %2 = load i32* @func_21_l_773, align 4, !tbaa !0
+  %tobool = icmp ne i32 %2, 0
+  br i1 %tobool, label %lbl_818, label %if.end
+
+if.end:                                           ; preds = %for.end
+  ret void
+}
+
+declare void @func_27(...)
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA", null}