llvm: Add support for "-fno-delete-null-pointer-checks"

Summary:
Support for this option is needed for building Linux kernel.
This is a very frequently requested feature by kernel developers.

More details : https://lkml.org/lkml/2018/4/4/601

GCC option description for -fdelete-null-pointer-checks:
This Assume that programs cannot safely dereference null pointers,
and that no code or data element resides at address zero.

-fno-delete-null-pointer-checks is the inverse of this implying that
null pointer dereferencing is not undefined.

This feature is implemented in LLVM IR in this CL as the function attribute
"null-pointer-is-valid"="true" in IR (Under review at D47894).
The CL updates several passes that assumed null pointer dereferencing is
undefined to not optimize when the "null-pointer-is-valid"="true"
attribute is present.

Reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk, srhines, void, george.burgess.iv

Reviewed By: efriedma, george.burgess.iv

Subscribers: eraman, haicheng, george.burgess.iv, drinkcat, theraven, reames, sanjoy, xbolva00, llvm-commits

Differential Revision: https://reviews.llvm.org/D47895

llvm-svn: 336613

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopVersioning/lcssa.ll b/llvm/test/Transforms/LoopVersioning/lcssa.ll
index 2cd4662c371..64993061008 100644
--- a/llvm/test/Transforms/LoopVersioning/lcssa.ll
+++ b/llvm/test/Transforms/LoopVersioning/lcssa.ll
@@ -33,3 +33,40 @@ bb3.loopexit:
 bb3:
   ret void
 }
+
+define void @fill_no_null_opt(i8** %ls1.20, i8** %ls2.21, i8* %cse3.22) #0 {
+; CHECK-LABEL: fill_no_null_opt(
+; CHECK: bb1.lver.check:
+; CHECK: %lver.safe = or i1 %memcheck.conflict, %{{.*}}
+; CHECK:  br i1 %lver.safe, label %bb1.ph.lver.orig, label %bb1.ph
+bb1.ph:
+  %ls1.20.promoted = load i8*, i8** %ls1.20
+  %ls2.21.promoted = load i8*, i8** %ls2.21
+  br label %bb1
+
+bb1:
+  %_tmp302 = phi i8* [ %ls2.21.promoted, %bb1.ph ], [ %_tmp30, %bb1 ]
+  %_tmp281 = phi i8* [ %ls1.20.promoted, %bb1.ph ], [ %_tmp28, %bb1 ]
+  %_tmp14 = getelementptr i8, i8* %_tmp281, i16 -1
+  %_tmp15 = load i8, i8* %_tmp14
+  %add = add i8 %_tmp15, 1
+  store i8 %add, i8* %_tmp281
+  store i8 %add, i8* %_tmp302
+  %_tmp28 = getelementptr i8, i8* %_tmp281, i16 1
+  %_tmp30 = getelementptr i8, i8* %_tmp302, i16 1
+  br i1 false, label %bb1, label %bb3.loopexit
+
+bb3.loopexit:
+  %_tmp30.lcssa = phi i8* [ %_tmp30, %bb1 ]
+  %_tmp15.lcssa = phi i8 [ %_tmp15, %bb1 ]
+  %_tmp28.lcssa = phi i8* [ %_tmp28, %bb1 ]
+  store i8* %_tmp28.lcssa, i8** %ls1.20
+  store i8 %_tmp15.lcssa, i8* %cse3.22
+  store i8* %_tmp30.lcssa, i8** %ls2.21
+  br label %bb3
+
+bb3:
+  ret void
+}
+
+attributes #0 = { "null-pointer-is-valid"="true" }