[InstCombineCalls] Use isKnownNonNullAt() to check nullness of gc.relocate return value

[• chenli]

Summary

This patch replaces isKnownNonNull() with isKnownNonNullAt() when checking nullness of gc.relocate return value. In this way it can handle cases where the relocated value does not have nonnull attribute but has a dominating null check from the CFG.

[reames]

LGTM w/minor comment addressed.

test/Transforms/InstCombine/gc.relocate.ll

26 ↗

(On Diff #34485)

I'd replace this vague check line with a bit of IR that will constant fold if the pointer is known non null. e.g. return (relocate == null);
; CHECK: ret i1 false

llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp

case Intrinsic::experimental_gc_relocate: {
     // TODO: provide a hook for this in GCStrategy.  There might be some weird
     // collector this property does not hold for.
     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 (isKnownNonNull(DerivedPtr))
+    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);
       }

llvm/trunk/test/Transforms/InstCombine/gc.relocate.ll

 ; CHECK-LABEL: @deref
 ; CHECK: call dereferenceable(8)
 entry:
     %load = load i32, i32 addrspace(1)* %dparam
     %tok = tail call i32 (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(i32 %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 i32 (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(i32 %tok,  i32 7, i32 7)
+    %cmp = icmp eq i32 addrspace(1)* %relocate, null
+    %ret_val = select i1 %cmp, i32 0, i32 1
+    ret i32 %ret_val
+}
+
+define i32 @implicit_nonnull(i32 addrspace(1)* %dparam) gc "statepoint-example" {
+; Checks that a nonnull pointer
+; CHECK-LABEL: @implicit_nonnull
+; CHECK: ret i32 1
+entry:
+    %cond = icmp eq i32 addrspace(1)* %dparam, null
+    br i1 %cond, label %no_gc, label %gc
+gc:
+    %load = load i32, i32 addrspace(1)* %dparam
+    %tok = tail call i32 (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(i32 %tok,  i32 7, i32 7)
+    %cmp = icmp eq i32 addrspace(1)* %relocate, null
+    %ret_val = select i1 %cmp, i32 0, i32 1
+    ret i32 %ret_val
+no_gc:
+    unreachable
+}