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, 124 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/phi-undef-loadstore.ll b/llvm/test/Transforms/SimplifyCFG/phi-undef-loadstore.ll
index c0f0046a1d2..e7e9e727346 100644
--- a/llvm/test/Transforms/SimplifyCFG/phi-undef-loadstore.ll
+++ b/llvm/test/Transforms/SimplifyCFG/phi-undef-loadstore.ll
@@ -31,6 +31,37 @@ if.end7:                                          ; preds = %if.else, %if.then4,
 ; CHECK: phi i32* [ %a, %if.then ], [ %c, %if.else ]
 }
 
+define i32 @test1_no_null_opt(i32* %a, i32 %b, i32* %c, i32 %d) nounwind #0 {
+entry:
+  %tobool = icmp eq i32 %b, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.else:                                          ; preds = %entry
+  %tobool3 = icmp eq i32 %d, 0
+  br i1 %tobool3, label %if.end7, label %if.then4
+
+if.then4:                                         ; preds = %if.else
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.end7:                                          ; preds = %if.else, %if.then4, %if.then
+  %x.0 = phi i32* [ %a, %if.then ], [ %c, %if.then4 ], [ null, %if.else ]
+  %tmp9 = load i32, i32* %x.0
+  ret i32 %tmp9
+
+; CHECK-LABEL: @test1_no_null_opt(
+; CHECK: if.then:
+; CHECK: if.else:
+; CHECK: if.then4:
+; CHECK: br label %if.end7
+; CHECK: if.end7:
+; CHECK-NEXT: phi i32* [ %a, %if.then ], [ %c, %if.then4 ], [ null, %if.else ]
+}
+
 define i32 @test2(i32* %a, i32 %b, i32* %c, i32 %d) nounwind {
 entry:
   %tobool = icmp eq i32 %b, 0
@@ -59,6 +90,35 @@ if.end7:                                          ; preds = %if.else, %if.then4,
 ; CHECK-NOT: phi
 }
 
+define i32 @test2_no_null_opt(i32* %a, i32 %b, i32* %c, i32 %d) nounwind #0 {
+entry:
+  %tobool = icmp eq i32 %b, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.else:                                          ; preds = %entry
+  %tobool3 = icmp eq i32 %d, 0
+  br i1 %tobool3, label %if.end7, label %if.then4
+
+if.then4:                                         ; preds = %if.else
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.end7:                                          ; preds = %if.else, %if.then4, %if.then
+  %x.0 = phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+  %tmp9 = load i32, i32* %x.0
+  ret i32 %tmp9
+; CHECK-LABEL: @test2_no_null_opt(
+; CHECK: if.then:
+; CHECK: if.else:
+; CHECK: if.then4:
+; CHECK: if.end7:
+; CHECK-NEXT: phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+}
+
 define i32 @test3(i32* %a, i32 %b, i32* %c, i32 %d) nounwind {
 entry:
   %tobool = icmp eq i32 %b, 0
@@ -86,6 +146,36 @@ if.end7:                                          ; preds = %if.else, %if.then4,
 ; CHECK: phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
 }
 
+define i32 @test3_no_null_opt(i32* %a, i32 %b, i32* %c, i32 %d) nounwind #0 {
+entry:
+  %tobool = icmp eq i32 %b, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.else:                                          ; preds = %entry
+  %tobool3 = icmp eq i32 %d, 0
+  br i1 %tobool3, label %if.end7, label %if.then4
+
+if.then4:                                         ; preds = %if.else
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.end7:                                          ; preds = %if.else, %if.then4, %if.then
+  %x.0 = phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+  tail call void @bar() nounwind
+  %tmp9 = load i32, i32* %x.0
+  ret i32 %tmp9
+; CHECK-LABEL: @test3_no_null_opt(
+; CHECK: if.then:
+; CHECK: if.else:
+; CHECK: if.then4:
+; CHECK: if.end7:
+; CHECK-NEXT: phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+}
+
 define i32 @test4(i32* %a, i32 %b, i32* %c, i32 %d) nounwind {
 entry:
   %tobool = icmp eq i32 %b, 0
@@ -113,3 +203,37 @@ if.end7:                                          ; preds = %if.else, %if.then4,
 ; CHECK-LABEL: @test4(
 ; CHECK-NOT: phi
 }
+
+define i32 @test4_no_null_opt(i32* %a, i32 %b, i32* %c, i32 %d) nounwind #0 {
+entry:
+  %tobool = icmp eq i32 %b, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.else:                                          ; preds = %entry
+  %tobool3 = icmp eq i32 %d, 0
+  br i1 %tobool3, label %if.end7, label %if.then4
+
+if.then4:                                         ; preds = %if.else
+  tail call void @bar() nounwind
+  br label %if.end7
+
+if.end7:                                          ; preds = %if.else, %if.then4, %if.then
+  %x.0 = phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+  %gep = getelementptr i32, i32* %x.0, i32 10
+  %tmp9 = load i32, i32* %gep
+  %tmp10 = or i32 %tmp9, 1
+  store i32 %tmp10, i32* %gep
+  ret i32 %tmp9
+; CHECK-LABEL: @test4_no_null_opt(
+; CHECK: if.then:
+; CHECK: if.else:
+; CHECK: if.then4:
+; CHECK: if.end7:
+; CHECK-NEXT: phi i32* [ %a, %if.then ], [ null, %if.then4 ], [ null, %if.else ]
+}
+
+attributes #0 = { "null-pointer-is-valid"="true" }