[test] Add test for null_pointer_is_valid and Inliner instsimplify interaction

[aeubanks]

Summary

As requested in D151254

[arsenm]

llvm/test/Transforms/Inline/instsimplify-null-pointer-is-valid.ll

4

Add comment explaining the test

[aeubanks]

add comment

[arsenm]

llvm/test/Transforms/Inline/instsimplify-null-pointer-is-valid.ll

24

Could also test what happens if the either the caller or callee is missing the attribute

[aeubanks]

add test where caller has null_pointer_is_valid but not callee
(vice versa is already tested to make sure it's not inlined)

llvm/test/Transforms/Inline/instsimplify-null-pointer-is-valid.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -passes=inline < %s -S | FileCheck %s
+
+; Test that instsimplify invoked by the inliner respects null_pointer_is_valid
+; (by ensuring that the instruction is inserted into the function when invoking
+; instsimplify).
+
+define internal i1 @f(ptr %p) null_pointer_is_valid {
+  %g = getelementptr inbounds i8, ptr %p, i32 -1
+  %r = icmp eq ptr %g, null
+  ret i1 %r
+}
+
+define i1 @g(ptr %p) null_pointer_is_valid {
+; CHECK-LABEL: define i1 @g
+; CHECK-SAME: (ptr [[P:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[G_I:%.*]] = getelementptr inbounds i8, ptr [[P]], i32 -1
+; CHECK-NEXT:    [[R_I:%.*]] = icmp eq ptr [[G_I]], null
+; CHECK-NEXT:    ret i1 [[R_I]]
+;
+  %r = call i1 @f(ptr %p)
+  ret i1 %r
+}
+
+define internal i1 @f2(ptr %p) {
+  %g = getelementptr inbounds i8, ptr %p, i32 -1
+  %r = icmp eq ptr %g, null
+  ret i1 %r
+}
+
+define i1 @g2(ptr %p) null_pointer_is_valid {
+; CHECK-LABEL: define i1 @g2
+; CHECK-SAME: (ptr [[P:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT:    [[G_I:%.*]] = getelementptr inbounds i8, ptr [[P]], i32 -1
+; CHECK-NEXT:    [[R_I:%.*]] = icmp eq ptr [[G_I]], null
+; CHECK-NEXT:    ret i1 [[R_I]]
+;
+  %r = call i1 @f2(ptr %p)
+  ret i1 %r
+}
+