[llvm] 24ae77e - [Attributor] Mark a non-defined `null` pointer as `noalias`

[Johannes Doerfert via llvm-commits]

Author: Johannes Doerfert
Date: 2020-01-28T23:09:37-06:00
New Revision: 24ae77eebffbf14ece11061cd4365f056fdaf426

URL: https://github.com/llvm/llvm-project/commit/24ae77eebffbf14ece11061cd4365f056fdaf426
DIFF: https://github.com/llvm/llvm-project/commit/24ae77eebffbf14ece11061cd4365f056fdaf426.diff

LOG: [Attributor] Mark a non-defined `null` pointer as `noalias`

If `null` is not defined we cannot access it, hence the pointer is
`noalias`. While this is not helpful on it's own it simplifies later
deductions that can skip over already known `noalias` pointers in
certain situations.

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/Attributor.cpp
    llvm/test/Transforms/Attributor/value-simplify.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 0598bca17ce7..306bfc43dce4 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -2417,8 +2417,9 @@ struct AANoAliasFloating final : AANoAliasImpl {
     Value &Val = getAssociatedValue();
     if (isa<AllocaInst>(Val))
       indicateOptimisticFixpoint();
-    if (isa<ConstantPointerNull>(Val) &&
-        Val.getType()->getPointerAddressSpace() == 0)
+    else if (isa<ConstantPointerNull>(Val) &&
+             !NullPointerIsDefined(getAnchorScope(),
+                                   Val.getType()->getPointerAddressSpace()))
       indicateOptimisticFixpoint();
   }
 
@@ -2496,6 +2497,11 @@ struct AANoAliasCallSiteArgument final : AANoAliasImpl {
     ImmutableCallSite ICS(&getAnchorValue());
     if (ICS.paramHasAttr(getArgNo(), Attribute::NoAlias))
       indicateOptimisticFixpoint();
+    Value &Val = getAssociatedValue();
+    if (isa<ConstantPointerNull>(Val) &&
+        !NullPointerIsDefined(getAnchorScope(),
+                              Val.getType()->getPointerAddressSpace()))
+      indicateOptimisticFixpoint();
   }
 
   /// See AbstractAttribute::updateImpl(...).

diff  --git a/llvm/test/Transforms/Attributor/value-simplify.ll b/llvm/test/Transforms/Attributor/value-simplify.ll
index b2563ad09be9..dff06e5262a4 100644
--- a/llvm/test/Transforms/Attributor/value-simplify.ll
+++ b/llvm/test/Transforms/Attributor/value-simplify.ll
@@ -210,7 +210,7 @@ define i32* @complicated_args_inalloca() {
 
 define internal void @test_sret(%struct.X* sret %a, %struct.X** %b) {
 ; CHECK-LABEL: define {{[^@]+}}@test_sret
-; CHECK-SAME: (%struct.X* nofree sret writeonly align 536870912 [[A:%.*]], %struct.X** nocapture nofree nonnull writeonly dereferenceable(8) [[B:%.*]])
+; CHECK-SAME: (%struct.X* noalias nofree sret writeonly align 536870912 [[A:%.*]], %struct.X** nocapture nofree nonnull writeonly dereferenceable(8) [[B:%.*]])
 ; CHECK-NEXT:    store %struct.X* [[A]], %struct.X** [[B]]
 ; CHECK-NEXT:    ret void
 ;
@@ -220,7 +220,7 @@ define internal void @test_sret(%struct.X* sret %a, %struct.X** %b) {
 define void @complicated_args_sret(%struct.X** %b) {
 ; CHECK-LABEL: define {{[^@]+}}@complicated_args_sret
 ; CHECK-SAME: (%struct.X** nocapture nofree writeonly [[B:%.*]])
-; CHECK-NEXT:    call void @test_sret(%struct.X* nofree writeonly align 536870912 null, %struct.X** nocapture nofree writeonly [[B]])
+; CHECK-NEXT:    call void @test_sret(%struct.X* noalias nofree writeonly align 536870912 null, %struct.X** nocapture nofree writeonly [[B]])
 ; CHECK-NEXT:    ret void
 ;
   call void @test_sret(%struct.X* null, %struct.X** %b)