Don't propagate dereferenceable attribute through gc.relocate in InstCombine

[apilipenko]

Summary

There is no need to propagate dereferenceable attribute through gc.relocate because isDereferenceableAndAligned pointer looks through relocations.

[reames]

LGTM - There's an argument that being able to stop the search earlier is desirable, but given how incomplete the handling is, just nuke it for now.

lib/Transforms/InstCombine/InstCombineCalls.cpp

if (isa<ConstantPointerNull>(DerivedPtr)) {
       // gc_relocate is uncasted. Use null-pointer of gc_relocate's type to replace it.
       return ReplaceInstUsesWith(*II, ConstantPointerNull::get(GCRelocateType));
     }
 
     // isKnownNonNull -> nonnull attribute
     if (isKnownNonNullAt(DerivedPtr, II, DT, TLI))
       II->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
 
-    // isDereferenceablePointer -> deref attribute
-    if (isDereferenceablePointer(DerivedPtr, DL)) {
-      if (Argument *A = dyn_cast<Argument>(DerivedPtr)) {
-        uint64_t Bytes = A->getDereferenceableBytes();
-        II->addDereferenceableAttr(AttributeSet::ReturnIndex, Bytes);
-      }
-    }
-
     // TODO: bitcast(relocate(p)) -> relocate(bitcast(p))
     // Canonicalize on the type from the uses to the defs
 
     // TODO: relocate((gep p, C, C2, ...)) -> gep(relocate(p), C, C2, ...)
   }
   }
 
   return visitCallSite(II);

test/Transforms/InstCombine/gc.relocate.ll

 ; RUN: opt < %s -instcombine -S | FileCheck %s
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 
 ; Uses InstCombine with DataLayout to propagate dereferenceable
 ; attribute via gc.relocate: if the derived ptr is dereferenceable(N),
 ; then the return attribute of gc.relocate is dereferenceable(N).
 
 declare zeroext i1 @return_i1()
 declare token @llvm.experimental.gc.statepoint.p0f_i1f(i64, i32, i1 ()*, i32, i32, ...)
 declare i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token, i32, i32)
 
-define i32 addrspace(1)* @deref(i32 addrspace(1)* dereferenceable(8) %dparam) gc "statepoint-example" {
-; Checks that a dereferenceabler pointer
-; CHECK-LABEL: @deref
-; CHECK: call dereferenceable(8)
-entry:
-    %load = load i32, i32 addrspace(1)* %dparam
-    %tok = tail call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %dparam)
-    %relocate = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token %tok,  i32 7, i32 7)
-    ret i32 addrspace(1)* %relocate
-}
-
 define i32 @explicit_nonnull(i32 addrspace(1)* nonnull %dparam) gc "statepoint-example" {
 ; Checks that a nonnull pointer
 ; CHECK-LABEL: @explicit_nonnull
 ; CHECK: ret i32 1
 entry:
     %load = load i32, i32 addrspace(1)* %dparam
     %tok = tail call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %dparam)
     %relocate = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token %tok,  i32 7, i32 7)