Add missing test for the "Don't delete empty preheaders" added in r265397

Author: Tom Jablin (tjablin)
llvm-svn: 265402

llvm/test/CodeGen/Generic/dont-remove-empty-preheader.ll

@@ -0,0 +1,39 @@
+; RUN: opt -codegenprepare -S < %s | FileCheck %s
+; CHECK: for.body.preheader
+
+@N = common global i32 0, align 4
+@E = common global i8** null, align 8
+@B = common global i8** null, align 8
+
+; Function Attrs: nounwind
+define i32 @foo() {
+entry:
+  %0 = load i32, i32* @N, align 4
+  %1 = load i8**, i8*** @E, align 8
+  %2 = load i8**, i8*** @B, align 8
+  %cmp7 = icmp eq i8** %2, %1
+  br i1 %cmp7, label %for.cond.cleanup, label %for.body.preheader
+
+for.body.preheader:                               ; preds = %entry
+  br label %for.body
+
+for.cond.cleanup.loopexit:                        ; preds = %for.body
+  %add.lcssa = phi i32 [ %add, %for.body ]
+  br label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup.loopexit, %entry
+  %n.0.lcssa = phi i32 [ %0, %entry ], [ %add.lcssa, %for.cond.cleanup.loopexit ]
+  ret i32 %n.0.lcssa
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %I.09 = phi i8** [ %incdec.ptr, %for.body ], [ %2, %for.body.preheader ]
+  %n.08 = phi i32 [ %add, %for.body ], [ %0, %for.body.preheader ]
+  %3 = load i8*, i8** %I.09, align 8
+  %call = tail call i32 @map(i8* %3)
+  %add = add nsw i32 %call, %n.08
+  %incdec.ptr = getelementptr inbounds i8*, i8** %I.09, i64 1
+  %cmp = icmp eq i8** %incdec.ptr, %1
+  br i1 %cmp, label %for.cond.cleanup.loopexit, label %for.body
+}
+
+declare i32 @map(i8*)