[llvm] [DA] use NSW arithmetic (PR #116632)

[Florian Hahn via llvm-commits]

================
@@ -0,0 +1,34 @@
+; RUN: opt < %s -disable-output "-passes=print<da>" -aa-pipeline=basic-aa
+
+; Check that the testcase does not crash the compiler.
+; https://github.com/llvm/llvm-project/issues/51512
+
+define void @func_1() {
+entry:
+  %l_83.i.i = alloca [2 x [5 x i32]], align 1
+  br label %for.cond857.preheader.i.i
+
+for.cond857.preheader.i.i:                        ; preds = %cleanup.cont1138.i.i, %entry
+  %l_89.08.i.i = phi i32 [ 0, %entry ], [ %add1140.i.i, %cleanup.cont1138.i.i ]
+  %0 = trunc i32 %l_89.08.i.i to i16
+  %1 = add i16 %0, 3
+  %arrayidx916.i.i = getelementptr inbounds [2 x [5 x i32]], [2 x [5 x i32]]* %l_83.i.i, i16 0, i16 %0, i16 %1
+  br label %for.body860.i.i
+
+for.body860.i.i:                                  ; preds = %for.body860.i.i, %for.cond857.preheader.i.i
+  %l_74.07.i.i = phi i32 [ 0, %for.cond857.preheader.i.i ], [ %add964.i.i, %for.body860.i.i ]
+  store i32 undef, i32* %arrayidx916.i.i, align 1
+  %2 = trunc i32 %l_74.07.i.i to i16
+  %arrayidx962.i.i = getelementptr inbounds [2 x [5 x i32]], [2 x [5 x i32]]* %l_83.i.i, i16 0, i16 %2, i16 %1
+  store i32 0, i32* %arrayidx962.i.i, align 1
+  %add964.i.i = add nuw nsw i32 %l_74.07.i.i, 1
+  br i1 false, label %for.body860.i.i, label %cleanup.cont1138.i.i
+
+cleanup.cont1138.i.i:                             ; preds = %for.body860.i.i
+  %add1140.i.i = add nuw nsw i32 %l_89.08.i.i, 1
+  %cmp602.i.i = icmp eq i32 %l_89.08.i.i, 0
+  br i1 %cmp602.i.i, label %for.cond857.preheader.i.i, label %for.cond1480.i.i.preheader
+
+for.cond1480.i.i.preheader:                       ; preds = %cleanup.cont1138.i.i
+  unreachable
----------------
fhahn wrote:

Should probably be `ret void`? Otherwise the function is always UB?

https://github.com/llvm/llvm-project/pull/116632