ValueTracking: Handle ptrmask in isKnownNeverZero

[arsenm]

Summary

The non-0 address space cases demonstrate the existing confused
behavior of nonnull for the underlying pointer argument.

[nikic]

This doesn't look correct to me. Consider something like ptrmask(ptr, 3) where ptr is nonnull align 4. The ptrmask result will always be a null pointer, even though both inputs are non-null.

[fhahn]

I think you'd need to also check that there's at least one common non-null bit for both pointer and mask.

[arsenm]

In D153753#4448500, @fhahn wrote:

I think you'd need to also check that there's at least one common non-null bit for both pointer and mask.

I got here because I wanted to handle this in computeKnownBits and was trying to craft a test, I guess I'll just directly do that instead

llvm/lib/Analysis/ValueTracking.cpp

if (auto *II = dyn_cast<IntrinsicInst>(I)) {
       case Intrinsic::fshr:
       case Intrinsic::fshl:
         // If Op0 == Op1, this is a rotate. rotate(x, y) != 0 iff x != 0.
         if (II->getArgOperand(0) == II->getArgOperand(1))
           return isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q);
         break;
       case Intrinsic::vscale:
         return true;
+      case Intrinsic::ptrmask:
+        return isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q) &&
+               isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q);
       default:
         break;
       }
     }
     break;
   }
 
   KnownBits Known(BitWidth);

llvm/test/Transforms/InstSimplify/nonnull-ptrmask.ll

;
   %masked = call ptr @llvm.ptrmask.p0.i32(ptr %arg, i32 %mask)
   %cmp = icmp eq ptr %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as0_ptrmask_constant_mask(ptr nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as0_ptrmask_constant_mask
 ; CHECK-SAME: (ptr nonnull [[ARG:%.*]]) {
-; CHECK-NEXT:    [[MASKED:%.*]] = call ptr @llvm.ptrmask.p0.i64(ptr [[ARG]], i64 -8)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[MASKED]], null
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %masked = call ptr @llvm.ptrmask.p0.i64(ptr %arg, i64 -8)
   %cmp = icmp eq ptr %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as0_ptrmask_constant_maski32(ptr nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as0_ptrmask_constant_maski32
 ; CHECK-SAME: (ptr nonnull [[ARG:%.*]]) {
-; CHECK-NEXT:    [[MASKED:%.*]] = call ptr @llvm.ptrmask.p0.i32(ptr [[ARG]], i32 -8)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[MASKED]], null
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %masked = call ptr @llvm.ptrmask.p0.i32(ptr %arg, i32 -8)
   %cmp = icmp eq ptr %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as0_ptrmask_mask0(ptr nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as0_ptrmask_mask0
;
   %masked = call ptr addrspace(10) @llvm.ptrmask.p10.i32(ptr addrspace(10) %arg, i32 %mask)
   %cmp = icmp eq ptr addrspace(10) %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as10_ptrmask_constant_mask(ptr addrspace(10) nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as10_ptrmask_constant_mask
 ; CHECK-SAME: (ptr addrspace(10) nonnull [[ARG:%.*]]) {
-; CHECK-NEXT:    [[MASKED:%.*]] = call ptr addrspace(10) @llvm.ptrmask.p10.i64(ptr addrspace(10) [[ARG]], i64 -8)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr addrspace(10) [[MASKED]], null
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %masked = call ptr addrspace(10) @llvm.ptrmask.p10.i64(ptr addrspace(10) %arg, i64 -8)
   %cmp = icmp eq ptr addrspace(10) %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as10_ptrmask_constant_maski32(ptr addrspace(10) nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as10_ptrmask_constant_maski32
 ; CHECK-SAME: (ptr addrspace(10) nonnull [[ARG:%.*]]) {
-; CHECK-NEXT:    [[MASKED:%.*]] = call ptr addrspace(10) @llvm.ptrmask.p10.i32(ptr addrspace(10) [[ARG]], i32 -8)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr addrspace(10) [[MASKED]], null
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %masked = call ptr addrspace(10) @llvm.ptrmask.p10.i32(ptr addrspace(10) %arg, i32 -8)
   %cmp = icmp eq ptr addrspace(10) %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as10_ptrmask_mask0(ptr addrspace(10) nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as10_ptrmask_mask0
;
   %masked = call ptr addrspace(2) @llvm.ptrmask.p2.i64(ptr addrspace(2) %arg, i64 %mask)
   %cmp = icmp eq ptr addrspace(2) %masked, null
   ret i1 %cmp
 }
 
 define i1 @nonnull_as2_ptrmask_constant_maski64(ptr addrspace(2) nonnull %arg) {
 ; CHECK-LABEL: define i1 @nonnull_as2_ptrmask_constant_maski64
 ; CHECK-SAME: (ptr addrspace(2) nonnull [[ARG:%.*]]) {
-; CHECK-NEXT:    [[MASKED:%.*]] = call ptr addrspace(2) @llvm.ptrmask.p2.i64(ptr addrspace(2) [[ARG]], i64 -8)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr addrspace(2) [[MASKED]], null
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %masked = call ptr addrspace(2) @llvm.ptrmask.p2.i64(ptr addrspace(2) %arg, i64 -8)
   %cmp = icmp eq ptr addrspace(2) %masked, null
   ret i1 %cmp
 }