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, 40 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/memcpy-addrspace.ll b/llvm/test/Transforms/InstCombine/memcpy-addrspace.ll
index 18615889dd8..b57a24e58b0 100644
--- a/llvm/test/Transforms/InstCombine/memcpy-addrspace.ll
+++ b/llvm/test/Transforms/InstCombine/memcpy-addrspace.ll
@@ -58,6 +58,23 @@ entry:
   ret void
 }
 
+; CHECK-LABEL: test_call_no_null_opt
+; CHECK: alloca
+; CHECK: call void @llvm.memcpy.p0i8.p2i8.i64
+; CHECK-NOT: addrspacecast
+; CHECK: call i32 @foo(i32* %{{.*}})
+define void @test_call_no_null_opt(i32 addrspace(1)* %out, i64 %x) #0 {
+entry:
+  %data = alloca [8 x i32], align 4
+  %0 = bitcast [8 x i32]* %data to i8*
+  call void @llvm.memcpy.p0i8.p2i8.i64(i8* align 4 %0, i8 addrspace(2)* align 4 bitcast ([8 x i32] addrspace(2)* @test.data to i8 addrspace(2)*), i64 32, i1 false)
+  %arrayidx = getelementptr inbounds [8 x i32], [8 x i32]* %data, i64 0, i64 %x
+  %1 = call i32 @foo(i32* %arrayidx)
+  %arrayidx1 = getelementptr inbounds i32, i32 addrspace(1)* %out, i64 %x
+  store i32 %1, i32 addrspace(1)* %arrayidx1, align 4
+  ret void
+}
+
 ; CHECK-LABEL: test_load_and_call
 ; CHECK: alloca
 ; CHECK: call void @llvm.memcpy.p0i8.p2i8.i64
@@ -80,6 +97,29 @@ entry:
   ret void
 }
 
+; CHECK-LABEL: test_load_and_call_no_null_opt
+; CHECK: alloca
+; CHECK: call void @llvm.memcpy.p0i8.p2i8.i64
+; CHECK: load i32, i32* %{{.*}}
+; CHECK: call i32 @foo(i32* %{{.*}})
+; CHECK-NOT: addrspacecast
+; CHECK-NOT: load i32, i32 addrspace(2)*
+define void @test_load_and_call_no_null_opt(i32 addrspace(1)* %out, i64 %x, i64 %y) #0 {
+entry:
+  %data = alloca [8 x i32], align 4
+  %0 = bitcast [8 x i32]* %data to i8*
+  call void @llvm.memcpy.p0i8.p2i8.i64(i8* align 4 %0, i8 addrspace(2)* align 4 bitcast ([8 x i32] addrspace(2)* @test.data to i8 addrspace(2)*), i64 32, i1 false)
+  %arrayidx = getelementptr inbounds [8 x i32], [8 x i32]* %data, i64 0, i64 %x
+  %1 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32 addrspace(1)* %out, i64 %x
+  store i32 %1, i32 addrspace(1)* %arrayidx1, align 4
+  %2 = call i32 @foo(i32* %arrayidx)
+  %arrayidx2 = getelementptr inbounds i32, i32 addrspace(1)* %out, i64 %y
+  store i32 %2, i32 addrspace(1)* %arrayidx2, align 4
+  ret void
+}
 
 declare void @llvm.memcpy.p0i8.p2i8.i64(i8* nocapture writeonly, i8 addrspace(2)* nocapture readonly, i64, i1)
 declare i32 @foo(i32* %x)
+
+attributes #0 = { "null-pointer-is-valid"="true" }