[InstCombine] More precise nuw preservation in ptrtoint of gep fold

We can transfer a nuw flag from the gep to the add. Additionally,
the inbounds + nneg case can be relaxed to nusw + nneg. Finally,
don't forget to pass the correct context instruction to
SimplifyQuery.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -2070,7 +2070,9 @@ Instruction *InstCombinerImpl::visitPtrToInt(PtrToIntInst &CI) {
         Base->getType() == Ty) {
       Value *Offset = EmitGEPOffset(GEP);
       auto *NewOp = BinaryOperator::CreateAdd(Base, Offset);
-      if (GEP->isInBounds() && isKnownNonNegative(Offset, SQ))
+      if (GEP->hasNoUnsignedWrap() ||
+          (GEP->hasNoUnsignedSignedWrap() &&
+           isKnownNonNegative(Offset, SQ.getWithInstruction(&CI))))
         NewOp->setHasNoUnsignedWrap(true);
       return NewOp;
     }

llvm/test/Transforms/InstCombine/cast_ptr.ll

@@ -342,6 +342,43 @@ define i32 @ptr_add_in_int_not_inbounds(i32 %x, i32 %y) {
   ret i32 %r
 }
 
+define i32 @ptr_add_in_int_nuw(i32 %x, i32 %y) {
+; CHECK-LABEL: @ptr_add_in_int_nuw(
+; CHECK-NEXT:    [[R:%.*]] = add nuw i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %ptr = inttoptr i32 %x to ptr
+  %p2 = getelementptr nuw i8, ptr %ptr, i32 %y
+  %r = ptrtoint ptr %p2 to i32
+  ret i32 %r
+}
+
+define i32 @ptr_add_in_int_nusw(i32 %x, i32 %y) {
+; CHECK-LABEL: @ptr_add_in_int_nusw(
+; CHECK-NEXT:    [[R:%.*]] = add i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %ptr = inttoptr i32 %x to ptr
+  %p2 = getelementptr nusw i8, ptr %ptr, i32 %y
+  %r = ptrtoint ptr %p2 to i32
+  ret i32 %r
+}
+
+define i32 @ptr_add_in_int_nusw_nneg(i32 %x, i32 %y) {
+; CHECK-LABEL: @ptr_add_in_int_nusw_nneg(
+; CHECK-NEXT:    [[NNEG:%.*]] = icmp sgt i32 [[Y:%.*]], -1
+; CHECK-NEXT:    call void @llvm.assume(i1 [[NNEG]])
+; CHECK-NEXT:    [[R:%.*]] = add nuw i32 [[X:%.*]], [[Y]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %nneg = icmp sge i32 %y, 0
+  call void @llvm.assume(i1 %nneg)
+  %ptr = inttoptr i32 %x to ptr
+  %p2 = getelementptr nusw i8, ptr %ptr, i32 %y
+  %r = ptrtoint ptr %p2 to i32
+  ret i32 %r
+}
+
 define i32 @ptr_add_in_int_const(i32 %x) {
 ; CHECK-LABEL: @ptr_add_in_int_const(
 ; CHECK-NEXT:    [[R:%.*]] = add nuw i32 [[X:%.*]], 4096