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ValueTracking: Fix isKnownNonZero for non-0 null pointers for byval

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The IR doesn't have a proper concept of invalid pointers, and "null"
constants are just all zeros (though it really needs one).

I think it's not possible to break this for AMDGPU due to the copy
semantics of byval. If you have an original stack object at 0, the
byval copy will be placed above it so I don't think it's really
possible to hit a 0 address.
This commit is contained in:
Matt Arsenault 2020-06-25 19:12:55 -04:00
parent 0ee3da9a31
commit bd9b22ee76
3 changed files with 53 additions and 4 deletions
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13
lib/Analysis/ValueTracking.cpp
View File

@ -2353,15 +2353,20 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
return false;
// Check for pointer simplifications.
if (V->getType()->isPointerTy()) {
if (PointerType *PtrTy = dyn_cast<PointerType>(V->getType())) {
// Alloca never returns null, malloc might.
if (isa<AllocaInst>(V) && Q.DL.getAllocaAddrSpace() == 0)
return true;
// A byval, inalloca, or nonnull argument is never null.
if (const Argument *A = dyn_cast<Argument>(V))
if (A->hasPassPointeeByValueAttr() || A->hasNonNullAttr())
// A byval, inalloca may not be null in a non-default addres space. A
// nonnull argument is assumed never 0.
if (const Argument *A = dyn_cast<Argument>(V)) {
if (((A->hasPassPointeeByValueAttr() &&
!NullPointerIsDefined(A->getParent(), PtrTy->getAddressSpace())) ||
A->hasNonNullAttr()))
return true;
}
// A Load tagged with nonnull metadata is never null.
if (const LoadInst *LI = dyn_cast<LoadInst>(V))

20
test/Transforms/InstSimplify/null-ptr-is-valid-attribute.ll Normal file
View File

@ -0,0 +1,20 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -instsimplify < %s | FileCheck %s
; A 0 valued byval pointer may be valid
define i1 @byval_may_be_zero(i32* byval(i32) %ptr) null_pointer_is_valid {
; CHECK-LABEL: @byval_may_be_zero(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32* [[PTR:%.*]], null
; CHECK-NEXT: ret i1 [[CMP]]
;
%cmp = icmp eq i32* %ptr, null
ret i1 %cmp
}
define i1 @nonnull_may_be_zero(i32* nonnull %ptr) null_pointer_is_valid {
; CHECK-LABEL: @nonnull_may_be_zero(
; CHECK-NEXT: ret i1 false
;
%cmp = icmp eq i32* %ptr, null
ret i1 %cmp
}

24
test/Transforms/InstSimplify/null-ptr-is-valid.ll Normal file
View File

@ -0,0 +1,24 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -instsimplify < %s | FileCheck %s
target datalayout = "A5"
; A 0 valued byval pointer may be valid
define i1 @byval_may_be_zero(i32 addrspace(5)* byval(i32) %ptr) {
; CHECK-LABEL: @byval_may_be_zero(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 addrspace(5)* [[PTR:%.*]], null
; CHECK-NEXT: ret i1 [[CMP]]
;
%cmp = icmp eq i32 addrspace(5)* %ptr, null
ret i1 %cmp
}
; FIXME: The interpretation of nonnull assumes a 0 pointer value, so
; this really is an incorrect fold.
define i1 @nonnull_may_be_zero(i32 addrspace(5)* nonnull %ptr) {
; CHECK-LABEL: @nonnull_may_be_zero(
; CHECK-NEXT: ret i1 false
;
%cmp = icmp eq i32 addrspace(5)* %ptr, null
ret i1 %cmp
}